Update Mullvad Browser release prep templates to include communications with downstream package maintainers

Merge Info

Related Issues

Backport Timeline

• Immediate - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)
• Next Minor Stable Release - patchset that needs to be verified in nightly before backport
• Eventually - patchset that needs to be verified in alpha before backport
• No Backport - patchset for the next major stable

Issue Tracking

• Link resolved issues with appropriate Release Prep issue for changelog generation

Change Description

So far we have (at least) the following downstream packages for Mullvad Browser being maintained:

• Linx:
  • arch - https://aur.archlinux.org/packages/mullvad-browser-bin
  • flatpack - https://github.com/flathub/flathub/pull/4052/commits
• macOS:
  • homebrew - https://github.com/Homebrew/homebrew-cask/blob/master/Casks/mullvad-browser.rb

Don't have the contact info yet for the homebrew maintainer but to keep it up to date would just require a version bump to the configuration.

/cc @ruihildt fyi