Use nightly for rustfmt checks in CI

Author: jessebraham

.github/workflows/ci.yml

@@ -171,7 +171,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      - uses: dtolnay/rust-toolchain@nightly
         with:
           components: rustfmt
       - uses: Swatinem/rust-cache@v2