feat: adding CI for updater tools

.github/workflows/updater_tools.yaml

@@ -0,0 +1,30 @@
+name: Updater Tools 💻
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+on:
+  pull_request:
+    paths:
+      - ".github/updater_tools.yaml"
+      - "updater_tools/lib/**"
+      - "updater_tools/test/**"
+      - "updater_tools/pubspec.yaml"
+  push:
+    branches:
+      - main
+    paths:
+      - ".github/updater_tools.yaml"
+      - "updater_tools/lib/**"
+      - "updater_tools/test/**"
+      - "updater_tools/pubspec.yaml"
+
+jobs:
+  semantic-pull-request:
+    uses: VeryGoodOpenSource/very_good_workflows/.github/workflows/semantic_pull_request.yml@v1
+
+  build:
+    uses: VeryGoodOpenSource/very_good_workflows/.github/workflows/dart_package.yml@v1
+    with:
+      working_directory: updater_tools

updater_tools/lib/src/extensions/arg_results.dart

@@ -4,6 +4,10 @@ import 'package:args/args.dart';
 
 /// Extension methods for validating options provided to [ArgResults].
 extension ArgResultsValidation on ArgResults {
+  /// Returns the value of the option with the given [name] as a [File].
+  ///
+  /// Throws an [ArgumentError] if the option is not present or if the file
+  /// does not exist.
   File asExistingFile(String name) {
     final file = File(this[name] as String);
     if (!file.existsSync()) {