Clippy: use stable toolchain

Author: ctz

.github/workflows/test.yaml

@@ -188,9 +188,8 @@ jobs:
         with:
           persist-credentials: false
       - name: Install rust toolchain
-        uses: dtolnay/rust-toolchain@master
+        uses: dtolnay/rust-toolchain@stable
         with:
-          toolchain: 1.70.0
           components: clippy
       - name: Check clippy
         # We allow unknown lints here because sometimes the nightly job