Master branch should change name to main

[pbiology]

What needs to be done:
The name "Master" isn't in use in best practices for GitHub anymore.

Suggestions on how to get it done:
Change it to "Main"

What are the arguments for getting it done:
Following best practices

Task is considered finished when:
Name is changed! :)

[JD2112]

@pbiology I create the "main" branch. Shall I set it to default?
@sofstam If the default branch changes to "main", will it impacts on the GH actions?

[sofstam]

@JD2112 Yes, it will impact. The GH action pull_request.yml should be changed to:

on:
  pull_request:
    branches:
    - main