Update actions/checkout action to v3 (#47)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/terraform.yaml

@@ -15,15 +15,15 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: hashicorp/setup-terraform@v1
       - run: make
 
   docs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           ref: ${{ github.event.pull_request.head.ref }}
       - uses: terraform-docs/gh-actions@v1