add rustfmt check to CI

Author: micolous

.github/workflows/rust.yml

@@ -10,6 +10,15 @@ env:
   CARGO_TERM_COLOR: always
 
 jobs:
+  rustfmt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: stable
+          components: rustfmt
+      - run: cargo fmt --check
   semver:
     runs-on: macos-11.0
     steps: