Update CI (#9)

* ci: Update to `actions/checkout@v3`.

* ci: Switch to `dtolnay/rust-toolchain`.

The `actions-rs` actions haven't been updated in some time and
result in a number of warnings about deprecated functionality
within GitHub Actions.

.github/workflows/rust.yml

@@ -16,17 +16,15 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
       with:
         submodules: true
 
     - name: Install Rust
-      uses: actions-rs/toolchain@v1
+      uses: dtolnay/rust-toolchain@master
       with:
-        profile: minimal
         toolchain: stable
-        override: true
-        components: rustfmt,clippy
+        components: rustfmt, clippy
 
     - name: Fix cargo cache permission issue
       run: sudo chown -R $(whoami):$(id -ng) ~/.cargo/