Not skip docker login on master (#2289)

* skip polkadot build on master

* not skip login in master

* typo

* docker login only on push and internal PRs

* missing ||

* not skip build on master

.github/workflows/build.yml

@@ -214,8 +214,12 @@ jobs:
         with:
           ref: ${{ needs.set-tags.outputs.git_ref }}
       - name: Login to DockerHub
-        # The if must stay on this step (because this job must not be skipped)
-        if: ${{ github.event.pull_request.head.repo.full_name == github.repository }}
+        # We should make sure that external PRs can't login to docker,
+        # but the check to detect if a PR is "external" not work when
+        # this workflow is trigerred by a push.
+        if: |
+          github.event_name == 'push' ||
+          github.event.pull_request.head.repo.full_name == github.repository
         uses: docker/[email protected]
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}