ci: make cache depend on branch

Author: frank-w

.github/workflows/build.yml

@@ -55,10 +55,9 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ~/.cache/ccache/
-          key: ${{ runner.os }}-ccache
+          key: ${{ runner.os }}-ccache-${{ github.ref_name }}
           restore-keys: |
-            ${{ runner.os }}-ccache
-            ${{ runner.os }}-ccache-
+            ${{ runner.os }}-ccache-${{ github.ref_name }}
 
       - name: Build for bananapi-r2
         run: |