【Flutter】「fatal error: module 'firebase_admob' not found」エラーでビルドできない

「FlutterアプリにFirebaseを追加するときハマったこと」を参考に、Runner/Runner ディレクトリにXcodeでGoogleService-Info.plistを追加しましたが、「fatal error: module 'firebase_admob' not found」エラーでビルドできませんでした。
解決方法をご教示いただけますと幸いです。

Running pod install...
Running Xcode build...
Xcode build done.                                            6.0s
Failed to build iOS app
Error output from Xcode build:
↳
    objc[21957]: Class AMSupportURLConnectionDelegate is implemented in both ?? (0x203ca8188) and ?? (0x1149a02b8). One of the two will be used. Which one is undefined.
    objc[21957]: Class AMSupportURLSession is implemented in both ?? (0x203ca81d8) and ?? (0x1149a0308). One of the two will be used. Which one is undefined.
    ** BUILD FAILED **


Xcode's output:
↳
    /Users/XXX/ios/Runner/GeneratedPluginRegistrant.m:10:9: fatal error: module 'firebase_admob' not found
    @import firebase_admob;
     ~~~~~~~^~~~~~~~~~~~~~
    1 error generated.
    note: Using new build system
    note: Building targets in parallel
    note: Planning build
    note: Constructing build description
    warning: Capabilities for Signing & Capabilities may not function correctly because its entitlements use a placeholder team ID. To resolve this, select a development team in the Runner editor. (in target 'Runner' from project 'Runner')

Could not build the application for the simulator.
Error launching application on iPhone 12 Pro Max.

実行環境

% flutter doctor -v
[✓] Flutter (Channel beta, 1.25.0-8.3.pre, on macOS 11.2 20D64 darwin-arm,
    locale ja-JP)
    • Flutter version 1.25.0-8.3.pre at /Users/libs/flutter
    • Framework revision 5d36f2e7f5 (3 weeks ago), 2021-01-14 15:57:49 -0800
    • Engine revision 7a8f8ca02c
    • Dart version 2.12.0 (build 2.12.0-133.7.beta)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Users/XXX/Library/Android/sdk
    • Platform android-30, build-tools 30.0.3
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.0

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      ???? https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      ???? https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.52.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension can be installed from:
      ???? https://marketplace.visualstudio.com/items?itemName=Dart-Code.flutter

[✓] Connected device (1 available)
    • iPhone 12 Pro Max (mobile) • 2AF7F633-95F8-43E8-89F1-385EE2463093 • ios •
      com.apple.CoreSimulator.SimRuntime.iOS-14-4 (simulator)

• No issues found!

pabspec.yaml

name: test
description: A new Flutter application.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev
version: 1.0.0+100

environment:
  sdk: ">=2.7.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^1.0.1
  url_launcher:
  firebase_core:
  firebase_admob: ^0.10.3
  flutter_launcher_icons: any


dev_dependencies:
  flutter_test:
    sdk: flutter
  integration_test:
    sdk: flutter

flutter:
  uses-material-design: true
  assets:
    - assets/images/