add macOS intel CI

[TheMrIron2]

macOS CI

Add macOS-15-intel CI alongside ubuntu-latest. Moved from #135

Installs requirements with brew and runs the toolchain script.

Additional fix - removed deprecated ::set-output in "Get short SHA".

[bucanero]

side note, once we merge ps3dev/PSL1GHT#162 we should be free from Python dependencies, as all tools would be native C code.

That should also help clean up a bit of the CI script I think, removing python installs.

[TheMrIron2]

Passing on Ubuntu and macOS CI now. Initial run failed due to a Savannah 502 in ps3libraries:

http://download.savannah.gnu.org/releases/freetype/freetype-old/freetype-2.4.3.tar.gz
2026-06-08T22:52:08.5596225Z Resolving download.savannah.gnu.org (download.savannah.gnu.org)... 209.51.188.200, 2001:470:142:5::200
2026-06-08T22:52:08.6156745Z Connecting to download.savannah.gnu.org (download.savannah.gnu.org)|209.51.188.200|:80... connected.
2026-06-08T22:52:08.6760398Z HTTP request sent, awaiting response... 502 Bad Gateway
2026-06-08T22:52:08.6760885Z 2026-06-08 22:52:08 ERROR 502: Bad Gateway.
2026-06-08T22:52:08.6761100Z 
2026-06-08T22:52:08.6767955Z ../scripts/004-freetype-2.4.3.sh: Failed.
2026-06-08T22:52:08.6770997Z ../scripts/009-ps3libraries.sh: Failed.

Resolved by re-running. Should be addressed at ps3libraries level, but is external to this PR.
I did not remove any Python while bringing up CI for the time being, as I wanted to prioritise stability with existing code. This is more likely a change for a separate PR.