Run CI for pushes to main

The GitHub workflow file mentioned the master branch, but it's called
main. Fixing this means we once again run CI on pushes to main.

Author: DigitalBrains1

.github/workflows/ci.yml

@@ -1,10 +1,10 @@
 name: CI
 
-# Trigger the workflow on all pull requests and pushes/merges to master branch
+# Trigger the workflow on all pull requests and pushes/merges to main branch
 on:
   pull_request:
   push:
-    branches: [master]
+    branches: [main]
 
 
 concurrency: