Add caching to checksum workflow

.github/workflows/checksum.yaml

@@ -46,6 +46,13 @@ jobs:
           echo "CHANGED_PKG=$(git diff --name-only origin/main origin/${GITHUB_HEAD_REF} "srcpkgs/*/template" | head -1 | cut -d/ -f2)" >> $GITHUB_ENV
           echo "CHANGED: ${{ env.CHANGED_PKG }}"
 
+      - name: cache upstream
+        uses: actions/cache@v4
+        id: cache-upstream
+        with:
+          path: upstream
+          key: void-templates-upstream-packages
+
       - name: checkout upstream templates
         uses: actions/checkout@v4
         with:
@@ -55,6 +62,7 @@ jobs:
           path: upstream
 
       - name: prep masterdir
+        if: steps.cache-upstream.outputs.cache-hit != 'true'
         working-directory: upstream
         run: |
           chown -R builder:builder . &&