CI (GH actions) workflow not triggered on pull request.

[brews]

Our currentCI workflow only triggers on push events. We need it to also trigger on pull request to main.

The addition should look something like this.

on:
  push:
    branches: "*"
  pull_request:
    branches: "main"

Should be an easy fix. We only triggered on push events because CI was just getting set up -- so we don't need to worry about breaking legacy behavior.

Stumbled across this in PR #2.