fix: correct buildkit cache read/write semantics per review

PR workflow:
- Use actions/cache/restore (restore-only) so PR builds never write
  new/stale cache entries on a cache miss
- Set skip-extraction: true so BuildKit mount cache is never written
  back on PR builds

Deploy workflow:
- Set skip-extraction: false so the canonical cache is always refreshed
  after each main-branch build
- Remove unused essentialcsharpweb-deploy scope from cache-from; that
  scope was never written to so it added no value

Author: BenjaminMichaelis

.github/workflows/Build-Test-And-Deploy.yml

@@ -78,7 +78,7 @@ jobs:
           builder: ${{ steps.buildx.outputs.name }}
           dockerfile: EssentialCSharp.Web/Dockerfile
           cache-dir: buildkit-cache
-          skip-extraction: ${{ steps.buildkit-cache.outputs.cache-hit }}
+          skip-extraction: false
 
       # Only build for dev registry — prod gets the image via az acr import in deploy-production
       - name: Build Container Image
@@ -91,9 +91,7 @@ jobs:
           secrets: |
             "nuget_pat=${{ secrets.AZURE_DEVOPS_PAT }}"
           outputs: type=docker,dest=${{ github.workspace }}/essentialcsharpwebimage.tar
-          cache-from: |
-            type=gha,scope=essentialcsharpweb-main
-            type=gha,scope=essentialcsharpweb-deploy
+          cache-from: type=gha,scope=essentialcsharpweb-main
           cache-to: type=gha,mode=max,scope=essentialcsharpweb-main
 
       - name: Upload artifact

.github/workflows/PR-Build-And-Test.yml

@@ -85,7 +85,7 @@ jobs:
         id: buildx
 
       - name: Restore BuildKit cache mounts
-        uses: actions/cache@v5
+        uses: actions/cache/restore@v5
         id: buildkit-cache
         with:
           path: buildkit-cache
@@ -98,7 +98,7 @@ jobs:
           builder: ${{ steps.buildx.outputs.name }}
           dockerfile: EssentialCSharp.Web/Dockerfile
           cache-dir: buildkit-cache
-          skip-extraction: ${{ steps.buildkit-cache.outputs.cache-hit }}
+          skip-extraction: true
 
       - name: Build Container Image
         uses: docker/build-push-action@v7