[ci] use host buildx config (#1015)

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **Chores**
- Improved Docker configuration handling during pull-request builds by
adding a setup step to preserve runner Docker credentials when present.
- Restricted container registry login to non-fork pull requests to avoid
using protected credentials for forked contributions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.github/workflows/pull-requests.yaml

@@ -32,7 +32,14 @@ jobs:
           fetch-depth: 0
           fetch-tags: true
 
+      - name: Set up Docker config
+        run: |
+          if [ -d ~/.docker ]; then
+            cp -r ~/.docker "${{ runner.temp }}/.docker"
+          fi
+
       - name: Login to GitHub Container Registry
+        if: ${{ !github.event.pull_request.head.repo.fork }}
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.OCIR_USER}}