msmtp: Fix build for Linux
msmtp: Fix build for Linux

- Gist logs from issue 13134: https://gist.github.com/CaptainQuirk/c7a1e0e8d51285ccb624766fda3f31d6
- This was failing to find the `libsecret` headers.
- Now use the new `uses_from_macos` syntax to specify dependencies to be
  installed on Linux.

msmtp: Remove 'cellar :any' bottle line for CI

Closes #14125.

Signed-off-by: Issy Long <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@issyl0.co.uk>

maxim-belkin/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core,LinuxbrewTestBot/homebrew-core