Avoid forks to perform releases when they receive tags

Before this, forks getting the tags pushed were performing
own releases of moodle-plugin-ci. Let's run that job only
for the root "moodlehq" one.

Author: stronk7

.github/workflows/release.yml

@@ -6,6 +6,8 @@ on:
 
 jobs:
   release:
+    # Avoid forks to perform this job.
+    if: github.repository_owner == 'moodlehq'
     name: Create Release
     runs-on: ubuntu-18.04