Actually *save*, not restore

Author: pcolby

.github/workflows/build.yaml

@@ -71,7 +71,7 @@ jobs:
           sudo apt update && sudo apt upgrade
           sudo apt install lcov llvm
       - name: Cache APT archives
-        uses: actions/cache/restore@v4
+        uses: actions/cache/save@v4
         with:
           path: /var/cache/apt/archives/*.deb
           key: ${{ runner.os }}-${{ runner.arch }}-apt-archives