Test PRs against all branches, not just main

Author: pgarrison

.github/workflows/ci.yml

@@ -7,8 +7,6 @@ on:
     tags:
       - "v*"
   pull_request:
-    branches:
-      - main
   schedule:
     # <minute [0,59]> <hour [0,23]> <day of the month [1,31]>
     # <month of the year [1,12]> <day of the week [0,6]>