Which branch should workflow files be located on for GitHub Actions to execute them?

Question

I have created on my main branch with

on:  
  push:
      branches: [ test ]

I have noticed, that while I can trigger it manually, and it will work, it will not actually trigger if I push to test. For that, I needed to create that same action file on test. Now, it seems like I don't even need to have the action on the main branch, is that correct?

So why does even the option so specify the branch that it should trigger on exist? It only triggers on the branches the file exists anyway. That said, I found it frustrating that I have to merge my one file from main to my test branch, is there a way to trigger the action automatically on push even if I do not have it on my test branch, only on main?