Prevent running twice for PRs from the same repo

Author: will-v-pi

.github/workflows/cmake.yml

@@ -7,7 +7,8 @@ env:
 
 jobs:
   build:
-    if: github.repository_owner == 'raspberrypi'
+    # Prevent running twice for PRs from same repo
+    if: github.repository_owner == 'raspberrypi' && (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name)
     runs-on: [self-hosted, Linux, X64]
     strategy:
       fail-fast: false