avoid double unit test runs on pr + push

Author: vandenman

.github/workflows/unittests.yml

@@ -12,6 +12,7 @@ jobs:
 
   unit-tests:
 
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name
     uses: jasp-stats/jasp-actions/.github/workflows/unittests.yml@master
     with:
       needs_JAGS:   true