Fix CCache config

Author: hannes-steffenhagen-diffblue

.github/workflows/pull-request-checks.yaml

@@ -18,7 +18,7 @@ jobs:
       # we'll keep 5 times that around per OS
       # to account for different versions/different
       # flags
-      # Bump so CI runs again 1
+      # Bump so CI runs again 2
       CCACHE_MAXSIZE: 500Mi
     steps:
       - uses: actions/checkout@v2
@@ -30,9 +30,12 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ~/.ccache
-          key: ${{ runner.os }}
+          key: ccache-${{ runner.os }}-${{ hashFiles('**') }}
+          restore-keys: ccache-${{ runner.os }}
       - name: Zero CCache statistics
-        run: ccache -z
+        run: |
+          ccache -s
+          ccache -z
       - name: Configure using CMake
         run: |
           mkdir build