Bump actions/checkout from 2 to 2.3.4

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](actions/checkout@v2...v2.3.4)

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
+        uses: actions/checkout@v2.3.4
       - name: Set up Go
         uses: actions/setup-go@v2
         with: