[ci] Fix build from external forks (#1530)

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

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## What this PR does


### Release note

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```release-note
[ci] Fix build from external forks
```

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## Summary by CodeRabbit

* **Chores**
  * Updated continuous integration workflow configuration.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.github/workflows/pull-requests.yaml

@@ -1,7 +1,8 @@
 name: Pull Request
 
 env:
-  REGISTRY: ${{ vars.OCIR_REPO }}
+  # TODO: unhardcode this
+  REGISTRY: iad.ocir.io/idyksih5sir9/cozystack
 on:
   pull_request:
     types: [opened, synchronize, reopened]