Fix typo in the Pull Request "build image" if. (#22585)

In case Pull request is run in the "apache/airflow" repository,
image building happens in the ci.yml workflow as of #22542.

However there was a typo in the build-image workflow that made the
images build in both - BuildImage and CI workflow.

GitOrigin-RevId: 16b0d244c74ea7fbb3056604148b3eeddabd60ea

.github/workflows/build-images.yml

@@ -166,7 +166,7 @@ jobs:
       fail-fast: true
     if: |
       needs.build-info.outputs.image-build == 'true' &&
-      github.event.pull_request.repo.head.full_name != 'apache/airflow'
+      github.event.pull_request.head.repo.full_name != 'apache/airflow'
     env:
       RUNS_ON: ${{ fromJson(needs.build-info.outputs.runsOn)[0] }}
       BACKEND: sqlite
@@ -254,7 +254,7 @@ jobs:
       fail-fast: true
     if: |
       needs.build-info.outputs.image-build == 'true' &&
-      github.event.pull_request.repo.head.full_name != 'apache/airflow'
+      github.event.pull_request.head.repo.full_name != 'apache/airflow'
     env:
       RUNS_ON: ${{ fromJson(needs.build-info.outputs.runsOn)[0] }}
       BACKEND: sqlite