[flutter_plugin_tools] Fix pubspec-check on Windows

script/tool/CHANGELOG.md

@@ -12,6 +12,7 @@
 - `license-check` now validates Kotlin files.
 - `pubspec-check` now checks that the description is of the pub-recommended
   length.
+- Fixed `pubspec-check` on Windows.
 
 ## 0.7.1
 

script/tool/lib/src/pubspec_check_command.dart

@@ -177,7 +177,7 @@ class PubspecCheckCommand extends PackageLoopingCommand {
       errorMessages.add('Missing "repository"');
     } else {
       final String relativePackagePath =
-          path.relative(package.path, from: packagesDir.parent.path);
+          getRelativePosixPath(package.directory, from: packagesDir.parent);
       if (!pubspec.repository!.path.endsWith(relativePackagePath)) {
         errorMessages
             .add('The "repository" link should end with the package path.');