Update issue-metrics.yml (#3962)

Author: ab5424

.github/workflows/issue-metrics.yml

@@ -9,6 +9,8 @@ permissions:
 
 jobs:
   build:
+    # prevent this action from running on forks
+    if: github.repository == 'materialsproject/pymatgen'
     name: issue metrics
     runs-on: ubuntu-latest
     permissions: