nicotine-plus: GTK4 variant does not work on older macOS

[barracuda156]

nicotine-plus works fine with GTK3 on older systems, but not with GTK4 (which is the default):

[04/10/24 17:35:43] Loading Python 3.11.9
[04/10/24 17:35:43] Loading Nicotine+ 3.3.2
[04/10/2024 17:35:48] Loading GTK 4.12.3
[04/10/2024 17:35:50] Loading plugin system
[04/10/2024 17:35:50] Loaded plugin Nicotine+ Commands
[04/10/2024 17:35:50] Listening on port: 6234
[04/10/2024 17:35:50] Connecting to server.slsknet.org:2242
No provider of glGenSamplers found.  Requires one of:
    Desktop OpenGL 3.3
    GL_ARB_sampler_objects
    OpenGL ES 3.0
Fatal Python error: Aborted

Thread 0xf4291000 (most recent call first):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/shares.py", line 1006 in process_scanner_messages
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/shares.py", line 1085 in _process_scanner
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 982 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1045 in _bootstrap_inner
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1002 in _bootstrap

Thread 0xf328f000 (most recent call first):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/selectors.py", line 566 in select
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/slskproto.py", line 2480 in _process_ready_sockets
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/slskproto.py", line 2713 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1045 in _bootstrap_inner
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1002 in _bootstrap

Thread 0xf228d000 (most recent call first):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/cli.py", line 93 in _handle_prompt
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/cli.py", line 57 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1045 in _bootstrap_inner
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1002 in _bootstrap

Thread 0xf1001000 (most recent call first):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/events.py", line 327 in _run_scheduler
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 982 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1045 in _bootstrap_inner
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/threading.py", line 1002 in _bootstrap

Current thread 0x00e10408 (most recent call first):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/gtkgui/widgets/window.py", line 78 in present
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/gtkgui/mainwindow.py", line 1233 in present
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/gtkgui/application.py", line 998 in on_activate
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gi/overrides/Gio.py", line 42 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/gtkgui/application.py", line 112 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/gtkgui/__init__.py", line 148 in run
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/pynicotine/__init__.py", line 223 in run
  File "/opt/local/bin/nicotine", line 34 in load_module
  File "/opt/local/bin/nicotine", line 38 in <module>

Extension modules: gnureadline, gi._gi, cairo._cairo, gi._gi_cairo (total: 4)
zsh: abort      nicotine
36-67% /opt/local/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/resource_tracker.py:254: UserWarning: resource_tracker: There appear to be 3 leaked semaphore objects to clean up at shutdown
  warnings.warn('resource_tracker: There appear to be %d '

Not sure what prevents GTK4 from working at the moment.

[mohd-akram (Mohamed Akram)]

Same as #70137.