ci: Explicitly install toolchain / activate cache for lint job

.github/workflows/style.yml

@@ -16,6 +16,13 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v2
+
+      - name: Install rust nightly toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly-2022-03-23
+          override: true
       - uses: Swatinem/rust-cache@v1
       - name: Check spelling
         uses: crate-ci/typos@master