add clippy to CI

Author: AaronKutch

.github/workflows/main.yml

@@ -102,13 +102,14 @@ jobs:
     - run: cargo generate-lockfile && ./ci/run-docker.sh ${{ matrix.target }}
       if: matrix.os == 'ubuntu-latest'
 
-  rustfmt:
-    name: Rustfmt
+  rustfmt-and-clippy:
+    name: Rustfmt and Clippy
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v1
       with:
         submodules: true
     - name: Install Rust
-      run: rustup update stable && rustup default stable && rustup component add rustfmt
+      run: rustup update stable && rustup default stable && rustup component add rustfmt && rustup component add clippy
     - run: cargo fmt -- --check
+    - run: cargo clippy -- -D clippy::all