Prepare multiprocessing handling 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 multiprocessing handling for python 3.14

salt/utils/platform.py

@@ -237,12 +237,16 @@ def is_aarch64():
 
 def spawning_platform():
     """
-    Returns True if multiprocessing.get_start_method(allow_none=False) returns "spawn"
+    Returns True if multiprocessing.get_start_method(allow_none=False) != "fork"
+    ("spawn" or "forkserver")
 
     This is the default for Windows Python >= 3.4 and macOS on Python >= 3.8.
     Salt, however, will force macOS to spawning by default on all python versions
+    Starting with Python 3.14, Linux also defaults to not "fork", but it uses
+    (new) "forkserver" instead of "spawn". Functionally, it's very similar as
+    far as Salt is concerned (process state is not inherited).
     """
-    return multiprocessing.get_start_method(allow_none=False) == "spawn"
+    return multiprocessing.get_start_method(allow_none=False) != "fork"
 
 
 def get_machine_identifier():