github-actions: Cache ccache per-job

Otherwise different jobs seem to overwrite each other, loosing part of
their cache.

Author: cwendling

.github/workflows/build.yml

@@ -162,6 +162,8 @@ jobs:
       # Setup ccache cache
       - name: ccache
         uses: hendrikmuhs/[email protected]
+        with:
+          key: ${{ github.job }}-${{ matrix.container }}-${{ matrix.cc }}
 
       # Cache the build of the mate-desktop dependency
       - name: Cache mate-desktop v${{env.MATE_PANEL_DEP}} dependency