Don't trigger wheel builds on forks (#11124)

Co-authored-by: hauntsaninja <>

Author: hauntsaninja

.github/workflows/build_wheels.yml

@@ -1,4 +1,4 @@
-name: Build wheels
+name: Trigger wheel build
 
 on:
   push:
@@ -14,6 +14,7 @@ on:
 
 jobs:
   build-wheels:
+    if: github.repository == 'python/mypy'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2