Test: Use a pup fork to make mac installer compatible with OS X 10.12.

[carlosperate]

Uses a proof of concept fork to see if it can create a macOS installer with wheels compatible with older macOS versions, 10.12+.

This is to test a possible solution to:

• Mu 1.2.0 fails to open in macOS 10.12 Sierra #2368

And the proof-of-concept PR in the pup repo that shows the difference between this fork and pup:

• Proof of concept: Add --pip-platform flag. pup#246

[carlosperate]

I can confirm the macOS installer from this PR works in OS X 10.12.

If the next Mu release comes before this feature lands in pup we might want to temporarily merge this PR and create the installers from this fork. We can always reverted back once pup has this functionality.

[carlosperate]

Merging this PR with the temporal workaround will also resolve issue:

• AppImage Debian Bullseye / Lubuntu 22.04 w/ X11 "Segmentation fault" #2318

Which was tested in Mu with PR:

• packaging: Install pup from the latest commit on GitHub to use Py 3.8.13 #2357

[carlosperate]

We'll merge this PR to be able to release Mu v1.2.1 with fixes for these two issues:

• Mu 1.2.0 fails to open in macOS 10.12 Sierra #2368
• AppImage Debian Bullseye / Lubuntu 22.04 w/ X11 "Segmentation fault" #2318

I've created this issue to remember to remove this workaround once pup has incorporated upstream fixes for those issues:

• Remove temp workaround (using pup fork for the Mu installers) when pup is updated #2392