PRs must also login to ghcr.io in order to read private images for the build process

(cherry picked from commit 04d891241b)

.github/workflows/reusable-docker-build.yml

@@ -113,9 +113,9 @@ jobs:
         uses: actions/checkout@v4
 
       # https://github.com/docker/login-action
+      # NOTE: This login occurs for BOTH non-PRs or PRs. PRs *must* also login to access private images from GHCR
+      # during the build process
       - name: Login to ${{ env.DOCKER_BUILD_REGISTRY }}
-        # Only login if not a PR, as PRs only trigger a Docker build and not a push
-        if: ${{ ! matrix.isPr }}
         uses: docker/login-action@v3
         with:
           registry: ${{ env.DOCKER_BUILD_REGISTRY }}