build(deps): Bump actions/checkout from 2 to 2.3.4 (#6456)

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/proto.yml

@@ -11,13 +11,13 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 4
     steps:
-      - uses: actions/checkout@master
+      - uses: actions/checkout@v2.3.4
       - name: lint
         run: make proto-lint
   proto-breakage:
     runs-on: ubuntu-latest
     timeout-minutes: 4
     steps:
-      - uses: actions/checkout@master
+      - uses: actions/checkout@v2.3.4
       - name: check-breakage
         run: make proto-check-breaking-ci