ci: simplify "on"

Jobs were only running when opening a pull request, not on subsequent pushes. There's also no need to exclude tags.

Author: Sjors

.github/workflows/ci.yml

@@ -1,9 +1,5 @@
 name: CI
-on:
-  pull_request:
-  push:
-    branches: ['**']
-    tags-ignore: ['**']
+on: [push]
 
 concurrency:
   group: ${{ github.event_name != 'pull_request' && github.run_id || github.ref }}