chore: Prevent Github action from running on forks (#1343)

Fixes #1342 🦕

Author: parthea

.github/workflows/main.yml

@@ -25,6 +25,8 @@ jobs:
   build:
     name: Update Discovery Artifacts PR
     runs-on: ubuntu-latest
+    if: |
+      ${{github.repository == 'googleapis/google-api-python-client'}}
     steps:
       - name: Get current date
         id: date