pythongh-90876: Prevent a multiprocessing import error.

Prevent `multiprocessing.spawn` from failing to *import* in environments
where `sys.executable` is `None`.  This regressed in 3.11 with the
addition of support for path-like objects in multiprocessing.

Author: gpshead

Lib/multiprocessing/spawn.py

@@ -35,7 +35,9 @@
 
 def set_executable(exe):
     global _python_exe
-    if sys.platform == 'win32':
+    if exe is None:
+        _python_exe = exe
+    elif sys.platform == 'win32':
         _python_exe = os.fsdecode(exe)
     else:
         _python_exe = os.fsencode(exe)

Misc/NEWS.d/next/Library/2023-07-05-13-08-23.gh-issue-90876.Qvlkfl.rst

@@ -0,0 +1,3 @@
+Prevent :mod:`multiprocessing.spawn` from failing to *import* in environments
+where ``sys.executable`` is ``None``.  This regressed in 3.11 with the addition
+of support for path-like objects in multiprocessing.