Bump actions/stale from 3 to 3.0.18

Bumps [actions/stale](https://github.com/actions/stale) from 3 to 3.0.18.
- [Release notes](https://github.com/actions/stale/releases)
- [Commits](https://github.com/actions/stale/compare/v3...v3.0.18)

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

.github/workflows/stale.yml

@@ -8,7 +8,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v3
+      - uses: actions/stale@v3.0.18
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
           days-before-stale: 21