Follow-up from "Support adding and removing labels w/ push opts"

The following discussion from !31831 (merged) should be addressed:

@ashmckenzie started a discussion:

There's a code quality degradation:

Method parse_options has a Cognitive Complexity of 8 (exceeds 5 allowed). Consider refactoring. in lib/gitlab/push_options.rb:51

Let's address in a follow-up Issue 🙂