Use $dartSdkVersion when creating "dummy" pubspec for create_api_docs (flutter#172327)

Closes flutter#70239.

/cc @ievdokdm

Author: matanlurey

dev/tools/create_api_docs.dart

@@ -284,7 +284,7 @@ class Configurator {
       'homepage: https://flutter.dev',
       'version: 0.0.0',
       'environment:',
-      "  sdk: '>=3.2.0-0 <4.0.0'",
+      "  sdk: '^${FlutterInformation.instance.getDartSdkVersion()}'",
       'dependencies:',
       for (final String package in findPackageNames(filesystem)) '  $package:\n    sdk: flutter',
       '  $kPlatformIntegrationPackageName: 0.0.1',
@@ -1194,6 +1194,9 @@ class FlutterInformation {
   /// Gets the name of the current branch in the Flutter framework in the repo.
   String getBranchName() => getFlutterInformation()['branchName']! as String;
 
+  /// Gets the current Dart SDK version.
+  Version getDartSdkVersion() => getFlutterInformation()['dartSdkVersion']! as Version;
+
   Map<String, Object>? _cachedFlutterInformation;
 
   /// Gets a Map of various kinds of information about the Flutter repo.

dev/tools/test/create_api_docs_test.dart

@@ -338,15 +338,13 @@ void main() {
     test('.generateConfiguration generates pubspec.yaml', () async {
       configurator.generateConfiguration();
       expect(packageRoot.childFile('pubspec.yaml').existsSync(), isTrue);
-      expect(packageRoot.childFile('pubspec.yaml').readAsStringSync(), contains('flutter_gpu:'));
-      expect(
-        packageRoot.childFile('pubspec.yaml').readAsStringSync(),
-        contains('dependency_overrides:'),
-      );
-      expect(
-        packageRoot.childFile('pubspec.yaml').readAsStringSync(),
-        contains('platform_integration:'),
-      );
+
+      final String pubspecContents = packageRoot.childFile('pubspec.yaml').readAsStringSync();
+
+      expect(pubspecContents, contains('flutter_gpu:'));
+      expect(pubspecContents, contains("sdk: '^2.14.0-360.0.dev'"));
+      expect(pubspecContents, contains('dependency_overrides:'));
+      expect(pubspecContents, contains('platform_integration:'));
     });
 
     test('.generateConfiguration generates fake lib', () async {