Bump grinder from 0.9.0 to 0.9.1 in /experimental/web_dashboard (#1064)

Bumps [grinder](https://github.com/google/grinder.dart) from 0.9.0 to 0.9.1.
- [Release notes](https://github.com/google/grinder.dart/releases)
- [Changelog](https://github.com/google/grinder.dart/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/grinder.dart/commits/0.9.1)

---
updated-dependencies:
- dependency-name: grinder
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

experimental/web_dashboard/pubspec.lock

@@ -337,7 +337,7 @@ packages:
       name: grinder
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.0"
+    version: "0.9.1"
   http_multi_server:
     dependency: transitive
     description: