Prepare salt.utils.process for python 3.14

Python 3.14 changed multiprocessing method from 'fork' to 'forkserver'
on Linux too:
python/cpython#84559

This leads to issue similar to when Python 3.8 changed it on Mac OS:
#57742

Change the condition to check for != 'fork' instead of == 'spawn'.

Author: marmarek

changelog/68148.changed.md

@@ -1 +1,2 @@
 Update packaged python from 3.10 to 3.11
+Fix salt.utils.process for python 3.14

salt/utils/process.py

@@ -897,7 +897,7 @@ def __new__(cls, *args, **kwargs):
         instance._finalize_methods = []
         instance.__logging_config__ = salt._logging.get_logging_options_dict()
 
-        if salt.utils.platform.spawning_platform():
+        if multiprocessing.get_start_method() != 'fork':
             # On spawning platforms, subclasses should call super if they define
             # __setstate__ and/or __getstate__
             instance._args_for_getstate = copy.copy(args)