Update actions/checkout requirement to v2.3.1

Updates the requirements on [actions/checkout](https://github.com/actions/checkout) to permit the latest version.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](28c7f3d2b5)

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

.github/workflows/docker.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code into the Go module directory
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2.3.1
 
       - name: Build and push Docker images
         uses: docker/build-push-action@v1.1.0

.github/workflows/go.yml

@@ -12,7 +12,7 @@ jobs:
           go-version: 1.14.x
 
       - name: Check out code into the Go module directory
-        uses: actions/checkout@v2
+        uses: actions/checkout@v2.3.1
 
       - name: Cache go module
         uses: actions/cache@v2