Changes the intermediate image building steps to use registry caching, allowig us to always rebuild them, but do so very quickly when nothing has changed

.github/workflows/reusable-ci-backend.yml

@@ -87,7 +87,7 @@ jobs:
       -
         name: Get changed files
         id: changed-files-specific
-        uses: tj-actions/changed-files@v18.1
+        uses: tj-actions/changed-files@v18.7
         with:
           files: |
             src/**