bpo-46720: Add support for path-like objects to multiprocessing.set_executable for Windows (GH-31279)

This bring the API to be on a par with Unix-like systems.

Lib/multiprocessing/util.py

@@ -450,7 +450,7 @@ def spawnv_passfds(path, args, passfds):
     errpipe_read, errpipe_write = os.pipe()
     try:
         return _posixsubprocess.fork_exec(
-            args, [os.fsencode(path)], True, passfds, None, None,
+            args, [path], True, passfds, None, None,
             -1, -1, -1, -1, -1, -1, errpipe_read, errpipe_write,
             False, False, None, None, None, -1, None)
     finally: