ci: nightly build for coverage

Author: da2ce7

.github/workflows/coverage.yaml

@@ -36,7 +36,7 @@ jobs:
 
       - id: setup
         name: Setup Toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@nightly
         with:
           toolchain: nightly
           components: llvm-tools-preview