editors/neovim: Update to 0.12.3

[dave_freedave.net]

Summary

There was an odd change to how the build generates lua code that now requires the use of luajit instead of lua51.

The diff makes clear what had to change to build.

Test Plan

make test is failing 2 tests, not sure if that is expected or not:

FAILED   2 tests, listed below:
FAILED   test/unit/testutil.lua @ 777: fs.c file permissions os_file_is_readable returns false if the file is not readable
...
FAILED   test/unit/testutil.lua @ 777: fs.c file permissions os_file_is_writable returns 0 if the file is readonly

I tried with neovim-0.12.2 prior to my changes and those tests fail the same way so maybe expected? Assuming @adamw will know.

[adamw]

Yeah, those failures are pre-existing. I'll get this testing. Thanks, Dave!

[adamw]

Excellent work, Dave! Thanks for this!