Bump actions/add-to-project from 0.4.0 to 0.6.0 (#3454)

Bumps [actions/add-to-project](https://github.com/actions/add-to-project) from 0.4.0 to 0.6.0.
- [Release notes](https://github.com/actions/add-to-project/releases)
- [Commits](actions/add-to-project@v0.4.0...v0.6.0)

---
updated-dependencies:
- dependency-name: actions/add-to-project
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

.github/workflows/milestoned_to_project.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/add-to-project@v0.4.0
+      - uses: actions/add-to-project@v0.6.0
         with:
           project-url: https://github.com/orgs/grafana/projects/135
           github-token: ${{ secrets.GH_BOT_ACCESS_TOKEN }}