Check formatting in CI

Author: seddonym

.github/workflows/main.yml

@@ -48,6 +48,9 @@ jobs:
           toolchain: stable
       - name: Print versions
         run: cargo version --verbose && cargo clippy --version
+      - name: Check formatting
+        run: cargo fmt --check
+        working-directory: ./rust
       - name: Run tests
         run: cargo test --no-default-features
         working-directory: ./rust