git push heroku master をするとエラー

rails (~> 5.2.3)
アプリケーションをherokuにデプロイする際に以下のエラーが表示されます。
エラー表示されるまでに行った内容としては
・Herokuのアカウントを作る
・

group :production do
  gem 'pg'
end

・.database.ymlの修正

production:
  <<: *default
  adapter: postgresql
  encoding: unicode
  pool: 5

・GitHubに反映
・インストールコマンド実行

% brew tap heroku/brew && brew install heroku

・インストール完了後、herokuのバージョンを確認することで、herokuがインストールされているか確認。

 % heloku -v
zsh: command not found: heloku

・~/.zshrcにherokuコマンドのパスを追記します。

vim ~/.zshrc
~/.zshrcに以下を追記
export PATH=$PATH:/usr/local/Cellar/heroku/7.39.5/libexec/bin

・sourceコマンドでzshrcの内容を反映する。

% source ~/.zshrc

% heroku -v
heroku/7.41.1 darwin-x64 node-v12.16.2

・PCからherokuにログインする

% heroku login
heroku: Press any key to open up the browser to login or q to exit:

・ターミナルからの操作でHerokuのアプリを作ります

% heroku create アプリ名

・.git/configを修正することでエラーを回避できます。

% vim .git/config

・以下を追記することで"heroku"がどこのURLを指すのか指定します。
アプリ名は上述の「heroku create アプリ名」で作成したアプリを記述

[remote "heroku"]
  url = https://git.heroku.com/アプリ名.git
  fetch = +refs/heads/*:refs/remotes/heroku/*

・デプロイ。

% git push heroku master

すると以下エラー

 my_app2 % git push heroku master
Enumerating objects: 870, done.
Counting objects: 100% (870/870), done.
Delta compression using up to 4 threads
Compressing objects: 100% (456/456), done.
Writing objects: 100% (870/870), 798.55 KiB | 28.52 MiB/s, done.
Total 870 (delta 500), reused 672 (delta 374), pack-reused 0
remote: Compressing source files... done.
remote: Building source:
remote: 
remote:  !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote:                         Detected buildpacks: Ruby,Node.js
remote:                         See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Installing bundler 2.0.2
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.5.1
remote: -----> Installing dependencies using bundler 2.0.2
remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote:        You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * pg
remote:        Bundler Output: You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * pg
remote: 
remote:  !
remote:  !     Failed to install gems via Bundler.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to myappoutput.
remote: 
To https://git.heroku.com/myappoutput.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/myappoutput.git'
Enumerating objects: 870, done.
Counting objects: 100% (870/870), done.
Delta compression using up to 4 threads
Compressing objects: 100% (456/456), done.
Writing objects: 100% (870/870), 798.55 KiB | 46.97 MiB/s, done.
Total 870 (delta 500), reused 672 (delta 374), pack-reused 0
remote: Compressing source files... done.
remote: Building source:
remote: 
remote:  !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote:                         Detected buildpacks: Ruby,Node.js
remote:                         See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Installing bundler 2.0.2
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.5.1
remote: -----> Installing dependencies using bundler 2.0.2
remote:        Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote:        You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * pg
remote:        Bundler Output: You are trying to install in deployment mode after changing
remote:        your Gemfile. Run `bundle install` elsewhere and add the
remote:        updated Gemfile.lock to version control.
remote:        
remote:        The dependencies in your gemfile changed
remote:        
remote:        You have added to the Gemfile:
remote:        * pg
remote: 
remote:  !
remote:  !     Failed to install gems via Bundler.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to outputmyapp.
remote: 
To https://git.heroku.com/outputmyapp.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/outputmyapp.git'

この件に関して改善策わかる方いましたらご教授お願いします