ci: bump actions/checkout from 2 to 2.3.4 (#517)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 2.3.4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v2...v2.3.4)

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

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

.github/workflows/label-commenter.yml

@@ -14,7 +14,7 @@ jobs:
   comment:
     runs-on: ubuntu-18.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
         with:
           ref: main