ci: Additional githubaction configuration (#3034)

- Pin action versions
- Dependabot to notify about action updates
- Update codeowners

.github/workflows/test-sql.yml

@@ -16,7 +16,7 @@ jobs:
         postgres-version: [ latest, 11-alpine, 12-alpine, 13-alpine, 14-alpine, 15-alpine ]
     name: SQL Tests ${{ matrix.postgres-version }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
       - name: Run SQL PgTap Tests
         run: |
           make test-sql POSTGRES_DOCKER_IMAGE_BASE=docker.mirror.hashicorp.services/postgres PG_DOCKER_TAG=${{ matrix.postgres-version }}