macOS demo simulation with (external) model library fails

Description

Simulation fails on macOS by not finding the model from a file containing the model.

I can reproduce the user report in https://forum.kicad.info/t/unable-to-simulate-the-demo-file-hv-converter/65356 as well.

With 9.0.6 on MS Windows 11 the simulation is o.k.

Steps to reproduce

1. Try to run demo at demos/simulation/gain_control
2. Try to run sim in project provided at https://forum.kicad.info/t/unable-to-simulate-the-demo-file-hv-converter/65356

KiCad Version

Application: KiCad Schematic Editor arm64 on arm64

Version: 9.0.6, release build

Libraries:
	wxWidgets 3.2.8
	FreeType 2.13.3
	HarfBuzz 10.1.0
	FontConfig 2.15.0
	libcurl/8.7.1 (SecureTransport) LibreSSL/3.3.6 zlib/1.2.12 nghttp2/1.64.0

Platform: macOS Sequoia Version 15.6.1 (Build 24G90), 64 bit, Little endian, wxMac
OpenGL: Apple, Apple M2, 2.1 Metal - 89.4

Build Info:
	Date: Oct 30 2025 15:39:55
	wxWidgets: 3.2.8 (wchar_t,wx containers)
	Boost: 1.87.0
	OCC: 7.8.1
	Curl: 8.7.1
	ngspice: 44.2
	Compiler: Clang 16.0.0 with C++ ABI 1002
	KICAD_IPC_API=ON