Replace unmaintained/outdated GitHub Actions (#17)

The `actions-rs/*` actions are replaced with `dtolnay/rust-toolchain`
and plain cargo commands.

.github/workflows/ci.yml

@@ -11,29 +11,14 @@ jobs:
           - stable
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
         with:
-          profile: minimal
           toolchain: ${{ matrix.rust }}
-          override: true
           components: rustfmt, clippy
 
-      - uses: actions-rs/cargo@v1
-        with:
-          command: build
-
-      - uses: actions-rs/cargo@v1
-        with:
-          command: test
-
-      - uses: actions-rs/cargo@v1
-        with:
-          command: fmt
-          args: --all -- --check
-
-      - uses: actions-rs/cargo@v1
-        with:
-          command: clippy
-          args: -- -D warnings
+      - run: cargo build
+      - run: cargo test
+      - run: cargo fmt --check --all
+      - run: cargo clippy -- -D warnings