Limit when release artifacts are built on forks.

Previously in #32114, adjustments were made to GHA workflow files to limit when workflows ran on forked repositories. But this missed the second job in the workflow that builds the release artifact.

Because it was set to always run even though the previous job is required, it has continued to run on forks.

.github/workflows/build-plugin-zip.yml

@@ -111,7 +111,7 @@ jobs:
         name: Build Release Artifact
         runs-on: ubuntu-latest
         needs: bump-version
-        if: always()
+        if: ${{ github.repository == 'WordPress/gutenberg' || github.event_name == 'pull_request' }}
 
         steps:
             - name: Checkout code