CI: Update workflow to run on any push and PR

Previously, the CI pipeline was only run on pushes
to a specific branch.
That branch does not exist anymore.
Rather it makes more sense to run the CI on any
push to the repository, as well as on any Pull
Request.

.github/workflows/ci.yml

@@ -1,9 +1,6 @@
 name: test
 
-on:
-  push:
-    branches:
-      - wip/testing
+on: [push, pull_request]
 
 jobs:
   build: