[ci] Use OCIR for non-release PRs

Changing the container registry from GHCR to OCIR will help with more
flexibe image retention policies and removes the restrictions on the
GitHub token when contributors submit PRs from forks. Release PRs remain
on GHCR, as before.

Signed-off-by: Timofei Larkin <lllamnyp@gmail.com>

.github/workflows/pull-requests.yaml

@@ -1,5 +1,7 @@
 name: Pull Request
 
+env:
+  REGISTRY: ${{ secrets.OCIR_REPO }}
 on:
   pull_request:
     types: [opened, synchronize, reopened]
@@ -33,9 +35,9 @@ jobs:
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with:
-          username: ${{ github.repository_owner }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-          registry: ghcr.io
+          username: ${{ secrets.OCIR_USER}}
+          password: ${{ secrets.OCIR_TOKEN }}
+          registry: iad.ocir.io
         env:
           DOCKER_CONFIG: ${{ runner.temp }}/.docker