ci: fix the gitlab trigger

There were two issues:

- ${{ }} converts the expression to a string and strings are apparently always truthy
  https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idif
- There was a typo in pr_data

Therefore, the check didn't work properly.

Signed-off-by: Ondřej Budai <ondrej@budai.cz>

.github/workflows/trigger-gitlab.yml

@@ -93,7 +93,7 @@ jobs:
           fi
 
       - name: Trigger GitLab nightly pipeline against this PR
-        if: ${{ env.GITLAB_TOKEN }} && ${{ steps.pr_date.outputs.pr_branch }}
+        if: env.GITLAB_TOKEN && steps.pr_data.outputs.pr_branch
         run: |
             # osbuild-composer
             PROJECT_ID=34771166