cache out dir

.github/workflows/build.yaml

@@ -21,11 +21,25 @@ jobs:
     - name: checkout submodule ref
       run: git submodule update --init --filter blob:none agnos-kernel-sdm845
 
-    - uses: hendrikmuhs/ccache-action@c92f40bee50034e84c763e33b317c77adaa81c92
+    - id: kernel-submodule
+      run: echo "ref=$(git ls-tree HEAD | awk '$4 == "agnos-kernel-sdm845"' | awk '{print $3}')" >> "$GITHUB_OUTPUT"
+
+    - uses: actions/cache/restore@v5
+      id: restore-cache
       with:
-        create-symlink: true
+        key: kernel-${{ steps.kernel-submodule.outputs.ref }}
+        path: agnos-kernel-sdm845/out
+        restore-keys: |
+          kernel-
 
     - run: ./build_kernel.sh
+
+    - uses: actions/cache/save@v5
+      if: always()
+      with:
+        key: ${{ steps.restore-cache.outputs.cache-primary-key }}
+        path: agnos-kernel-sdm845/out
+
     - uses: actions/upload-artifact@v4
       with:
         name: boot.img