Enable CI for non-master branches

This eases development in fork repositories, in particular.

Signed-off-by: Sebastian Pipping <sebastian@pipping.org>

Author: hartwork

.github/workflows/cmake-multi-platform.yml

@@ -4,9 +4,7 @@ name: CMake on multiple platforms
 
 on:
   push:
-    branches: [ "master" ]
   pull_request:
-    branches: [ "master" ]
   schedule:
     - cron: '0 2 * * 5'  # Every Friday at 2am