Bump actions/checkout from 2.3.5 to 2.4.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.3.5 to 2.4.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2.3.5...v2.4.0)

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

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

.github/workflows/main.yml

@@ -19,7 +19,7 @@ jobs:
       KRB5_CONFIG: /home/runner/work/tsig/tsig/testdata/docker/krb5.conf
     steps:
       - name: Checkout
-        uses: actions/checkout@v2.3.5
+        uses: actions/checkout@v2.4.0
       - name: Set up Go
         uses: actions/setup-go@v2
         with: