ci: Run on macOS

[hyperupcall]

related: fixes #xxx

How to test pre-release?

☠️ Feature can be unstable and break your prompt!

fisher install pure-fish/pure@feat/foo_feature # branch name
set --universal pure_enable_foo_feature true

First contribution?

Check the 👍 Contribute section and the contributing guide.

Acceptance Checks

• documentation is up-to-date:
  • features list ;
  • Prompt Symbol ;
  • 🔌 Features' Flags ;
• feature flag is present in conf.d/pure.fish ;
• symbol is present in conf.d/pure.fish ;
• tests are passing (I can help you 🤗 ):
  • config are tested (cf. tests/_pure.test.fish) ;
  • feature is covered ;
• customization is available ;
• feature is implemented.