Bump github/issue-metrics from 3.20.1 to 3.21.0

Bumps [github/issue-metrics](https://github.com/github/issue-metrics) from 3.20.1 to 3.21.0.
- [Release notes](https://github.com/github/issue-metrics/releases)
- [Commits](119b5237f4...346541fd00)

---
updated-dependencies:
- dependency-name: github/issue-metrics
  dependency-version: 3.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/issue-metrics.yml

@@ -35,7 +35,7 @@ jobs:
         echo "last_month=$first_day..$last_day" >> "$GITHUB_ENV"
 
     - name: Run issue-metrics tool
-      uses: github/issue-metrics@119b5237f41e78241b9b9cae254e544b52a359a0 # v3.20.1
+      uses: github/issue-metrics@346541fd0068df64c02607a4c7f55438dc2881e2 # v3.21.0
       env:
         GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         SEARCH_QUERY: 'repo:FreeCAD/FreeCAD is:issue created:${{ env.last_month }}'