Ensure we use "pr-testing" images for PRs, but use "latest" images fo…

…r other builds (e.g. after PR is merged to a branch).

.github/workflows/docker.yml

@@ -161,9 +161,10 @@ jobs:
     env:
       # Override defaults dspace.server.url because backend starts at http://127.0.0.1:8080
       dspace__P__server__P__url: http://127.0.0.1:8080/server
-      # Force using "pr-testing" version of all Docker images. The "pr-testing" tag is a temporary tag that we
-      # assign to all PR-built docker images in reusabe-docker-build.yml
-      DSPACE_VER: pr-testing
+      # If this is a PR, force using "pr-testing" version of all Docker images. Otherwise, for branch commits, use the
+      # "latest" tag. NOTE: the "pr-testing" tag is a temporary tag that we assign to all PR-built docker images in
+      # reusabe-docker-build.yml
+      DSPACE_VER: ${{ github.event_name == 'pull_request' && 'pr-testing' || 'latest' }}
     steps:
       # Checkout our codebase (to get access to Docker Compose scripts)
       - name: Checkout codebase