Update cmake workflow to trigger on push + pull request. Only run in raspberry pi repo (not on forks)

Author: liamfraser

.github/workflows/cmake.yml

@@ -1,12 +1,13 @@
 name: CMake
-on: [push]
+on: [push, pull_request]
 
 env:
   # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
   BUILD_TYPE: Release
 
 jobs:
   build:
+    if: github.repository_owner == 'raspberrypi'
     runs-on: [self-hosted, Linux, X64]
 
     steps: