Change grabclipboard() to use PNG compression on macOS

[abey79]

This PR changes grabclipboard() to use a PNG compression instead of a lossy JPG compression when reading images from he clipboard on macOS.

Fixes #7214

[radarhere]

A note for the future - our tradition is to not include the CHANGES.rst updates in PRs. If something else were to be merged in first, it would create a conflict.

I've created abey79#1 with a suggestion.

[abey79]

Thanks for the fix, quite the overlook on my part.

As for CHANGES.rst, it's noted. Maybe .github/CONTRIBUTING.md might be reworded? I tried to comply to the following based on recent commits I found:

• Include release notes as needed or appropriate with your bug fixes, feature additions and tests.

[hugovk]

Thanks!

[radarhere]

As for CHANGES.rst, it's noted. Maybe .github/CONTRIBUTING.md might be reworded? I tried to comply to the following based on recent commits I found:

• Include release notes as needed or appropriate with your bug fixes, feature additions and tests.

Ok, I've created PR #7220