Enable CI for pull requests (including downstream)

Author: bxsx

.github/workflows/ci.yml

@@ -7,11 +7,12 @@
 # @see https://github.com/nektos/act/issues/329
 name: Rollbar-PHP-Laravel CI
 
-# Fire this action on pushes to main branch (master) as well as pull requests
-# (push: without any configuration assumes this). Also, run every day at 02:42
-# GMT -- this catches failures from dependencies that update indepdently.
+# Fire this action on pushes to main branch (master) as well as other branches
+# or pull requests. Also, run every day at 02:42 GMT -- this catches failures
+# from dependencies that update indepdently.
 on:
   push:
+  pull_request:
   schedule:
     - cron: '42 2 * * *'