ci: Build pull requests, too

Build pull requests, just like we build on every push.

Author: flaix

.github/workflows/ci-build.yml

@@ -1,10 +1,14 @@
-name: Continous build on every push
+name: Continous integration
 
 on:
   push:
     branches-ignore:
       - 'release*'
       - gh-pages
+  pull_request:
+    branches-ignore:
+      - 'release*'
+      - gh-pages
 
 jobs:
   build_linux: