Fix version check tests

script/tool/lib/src/version_check_command.dart

@@ -6,6 +6,7 @@ import 'package:file/file.dart';
 import 'package:git/git.dart';
 import 'package:http/http.dart' as http;
 import 'package:meta/meta.dart';
+import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:pubspec_parse/pubspec_parse.dart';
 
@@ -178,8 +179,13 @@ ${indentation}HTTP response: ${pubVersionFinderResponse.httpResponse.body}
     required GitVersionFinder gitVersionFinder,
   }) async {
     final File pubspecFile = package.childFile('pubspec.yaml');
-    return await gitVersionFinder.getPackageVersion(
-        path.relative(pubspecFile.absolute.path, from: (await gitDir).path));
+    final String relativePath =
+        path.relative(pubspecFile.absolute.path, from: (await gitDir).path);
+    // Use Posix-style paths for git.
+    final String gitPath = path.style == p.Style.windows
+        ? p.posix.joinAll(path.split(relativePath))
+        : relativePath;
+    return await gitVersionFinder.getPackageVersion(gitPath);
   }
 
   /// Returns true if the version of [package] is either unchanged relative to

script/tool/test/lint_podspecs_command_test.dart

@@ -9,7 +9,6 @@ import 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_plugin_tools/src/common/core.dart';
 import 'package:flutter_plugin_tools/src/lint_podspecs_command.dart';
-import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
 import 'mocks.dart';