Merge pull request #279 from tevador/pr-ci1

Avoid redundant CI runs

.github/workflows/c-cpp.yml

@@ -1,6 +1,9 @@
 name: C/C++ CI
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [ master ]
+  pull_request:
 
 jobs:
   build-alpine: