ci: update CI workflow to trigger on pull requests to main branch

* Changed the branch from master to main for pull request triggers
* Removed push trigger for consistency with current branching strategy

Author: michaelpporter

.github/workflows/ci.yml

@@ -2,9 +2,8 @@ name: CI
 
 on:
     pull_request:
-    push:
         branches:
-            - master
+            - main
 
 jobs:
     test: