[Flutter][Xcode]CocoaPods 1.12.1 out of date (1.13.0 is recommended).エラー

## はじめに
Flutterのアップグレードを実行したところ、flutter doctorでXcodeのcocoapodエラーが出たので対処法を備忘録メモ。

```
% flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.19.5, on macOS 14.4.1 23E224 darwin-arm64,
    locale ja-JP)
[✓] Android toolchain - develop for Android devices (Android SDK version
    32.1.0-rc1)
[!] Xcode - develop for iOS and macOS (Xcode 15.3)
    ! CocoaPods 1.12.1 out of date (1.13.0 is recommended).
        CocoaPods is used to retrieve the iOS and macOS platform side's plugin
        code that responds to your plugin usage on the Dart side.
        Without CocoaPods, plugins will not work on iOS or macOS.
        For more info, see https://flutter.dev/platform-plugins
      To upgrade see
      https://guides.cocoapods.org/using/getting-started.html#updating-cocoapo
      ds for instructions.
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.2)
[✓] Android Studio (version 2022.2)
[✓] VS Code (version 1.84.2)
[✓] Connected device (3 available)
[✓] Network resources
```

## 原因
読んだままでcocoapodのバージョンを1.13.0を推奨してるとのこと。
つまりは単なるcocoapodのバージョンあげれば良いということです。
xcodeでios開発をしてもcocoapodの存在を忘れかけていました。

## 解決策

エラーに出ている対応策の公式ページに記載されています
https://guides.cocoapods.org/using/getting-started.html#updating-cocoapo

cocoapodは既に入っているわけなのでアップグレード
```
[sudo] gem install cocoapods
```

実行結果
```
% sudo gem install cocoapods
Password:
Ignoring nio4r-2.5.8 because its extensions are not built. Try: gem pristine nio4r --version 2.5.8
Ignoring racc-1.6.0 because its extensions are not built. Try: gem pristine racc --version 1.6.0
Ignoring unf_ext-0.0.8 because its extensions are not built. Try: gem pristine unf_ext --version 0.0.8
Ignoring websocket-driver-0.7.5 because its extensions are not built. Try: gem pristine websocket-driver --version 0.7.5
Fetching typhoeus-1.4.1.gem
Fetching xcodeproj-1.24.0.gem
Fetching cocoapods-downloader-2.1.gem
Fetching ffi-1.16.3.gem
Fetching cocoapods-core-1.15.2.gem
Fetching cocoapods-1.15.2.gem
Successfully installed xcodeproj-1.24.0
Successfully installed cocoapods-downloader-2.1
Building native extensions. This could take a while...
Successfully installed ffi-1.16.3
Successfully installed ethon-0.16.0
Successfully installed typhoeus-1.4.1
Successfully installed httpclient-2.8.3
A new major version is available for Algolia! Please now use the https://rubygems.org/gems/algolia gem to get the latest features.
Successfully installed algoliasearch-1.27.5
Successfully installed fuzzy_match-2.0.4
Successfully installed cocoapods-core-1.15.2
Successfully installed cocoapods-1.15.2
Parsing documentation for xcodeproj-1.24.0
Installing ri documentation for xcodeproj-1.24.0
Parsing documentation for cocoapods-downloader-2.1
Installing ri documentation for cocoapods-downloader-2.1
Parsing documentation for ffi-1.16.3
Installing ri documentation for ffi-1.16.3
Parsing documentation for ethon-0.16.0
Installing ri documentation for ethon-0.16.0
Parsing documentation for typhoeus-1.4.1
Installing ri documentation for typhoeus-1.4.1
Parsing documentation for httpclient-2.8.3
Installing ri documentation for httpclient-2.8.3
Parsing documentation for algoliasearch-1.27.5
Installing ri documentation for algoliasearch-1.27.5
Parsing documentation for fuzzy_match-2.0.4
Installing ri documentation for fuzzy_match-2.0.4
Parsing documentation for cocoapods-core-1.15.2
Installing ri documentation for cocoapods-core-1.15.2
Parsing documentation for cocoapods-1.15.2
Installing ri documentation for cocoapods-1.15.2
Done installing documentation for xcodeproj, cocoapods-downloader, ffi, ethon, typhoeus, httpclient, algoliasearch, fuzzy_match, cocoapods-core, cocoapods after 19 seconds
10 gems installed
```

無事にできたか確認します
```
% flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.19.5, on macOS 14.4.1 23E224 darwin-arm64,
    locale ja-JP)
[✓] Android toolchain - develop for Android devices (Android SDK version
    32.1.0-rc1)
[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.2)
[✓] Android Studio (version 2022.2)
[✓] VS Code (version 1.84.2)
[✓] Connected device (3 available)
[✓] Network resources
```

OK

## さいごに
Flutterのupgradeすると大体Android(jvmなど)かXcodeのバージョン違いのエラーが出ます。
エラーを見ると解決方法のサイトを示していることが多いので大体はそれで解決します。
今回のFlutterアップデートで2月16日リリースの「Flutter 3.19」と「Dart 3.3」となりました。Dart3.3はプラットフォームにWebを入れた際に互換性問題などが指摘さていますが、とりあえずextension typeでラッパークラスが自作できるようになったのでメリットは大きいのではないでしょうか。

参考記事
https://forest.watch.impress.co.jp/docs/news/1569386.html