ci: change cache key for macOS sccache

In hopes that it yields cache hits.

Author: indygreg

.github/workflows/macos.yml

@@ -29,7 +29,7 @@ jobs:
             ~/.cargo/registry
             ~/.cargo/git
             target
-          key: ${{ runner.os }}-sccache-${{ hashFiles('Cargo.lock') }}
+          key: ${{ runner.os }}-sccache-${{ hashFiles('Cargo.lock') }}-0
 
       - name: Build sccache
         run: |