[Godot4] fix macOS CI

[touilleMan]

https://github.com/touilleMan/godot-python/runs/7530366434?check_suite_focus=true#step:7:808

ERROR: Can't open dynamic library: /private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/godot-python-test-i93xfgzx/addons/pythonscript/macos-x86_64/libpythonscript.dylib, error: dlopen(/private/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/godot-python-test-i93xfgzx/addons/pythonscript/macos-x86_64/libpythonscript.dylib, 2): Library not loaded: /install/lib/libpython3.9.dylib

This is most likely due to the rpath configuration

godot-python/src/meson.build

Lines 156 to 167 in e68d3fd

	if host_platform.startswith('linux')
	lib_pythonscript_rpath = '$ORIGIN/lib'
	elif host_platform.startswith('macos')
	lib_pythonscript_rpath = '@loader_path/lib'
	endif
	lib_pythonscript = shared_library(
	'pythonscript',
	['pythonscript.c'],
	dependencies: [dep_godot, dep_python, dep__pythonscript],
	install_rpath: lib_pythonscript_rpath, # To find libpython