CI: Use full version number for actions/checkout

Author: Turbo87

.github/workflows/coverage.yml

@@ -38,7 +38,7 @@ jobs:
           - 5432:5432
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v3.0.0
 
       # Set up Rust
       - run: rustup default ${{ env.RUST_VERSION }}