Add test checking that Cargo.lock file is up to date

.github/workflows/rust-tests.yml

@@ -31,6 +31,9 @@ jobs:
       - name: Check formatting
         run: cargo fmt -- --check
 
+      - name: Check Cargo.lock up to date
+        run: cargo update -w --frozen
+
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}