ci: Split GitHub Actions ccache per job

Author: cwendling

.github/workflows/build.yml

@@ -104,6 +104,8 @@ jobs:
       # Setup ccache cache
       - name: ccache
         uses: hendrikmuhs/[email protected]
+        with:
+          key: ${{ matrix.container }}-${{ matrix.cc }}
 
       # Follows regular build and test steps