[master] Allow Homebrew package manager in all systems but Windows

[cdalvaro]

What does this PR do?

This PR removes the restriction for using mac_brew_pkg module only on macOS systems, since Homebrew can be run in Linux too: https://docs.brew.sh/Homebrew-on-Linux

I think that the module could be renamed to brew_pkg instead of mac_brew_pkg. But I need some help here to understand what changes are needed for this to be made.

Merge requirements satisfied?

• [x] Docs
• [x] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [x] Tests written/updated

Commits signed with GPG?

Yes

Please review Salt's Contributing Guide for best practices, including the PR Guidelines.

See GitHub's page on GPG signing for more information about signing commits with GPG.