Add multiprocessing.popen_spawn_win32 submodule (#8428)

tests/stubtest_allowlists/darwin.txt

@@ -48,6 +48,9 @@ winsound
 ossaudiodev
 spwd
 
+# multiprocessing.popen_spawn_win32 exists on Darwin but fail to import
+multiprocessing.popen_spawn_win32
+
 # Platform differences that cannot be captured by the type system
 os.SCHED_[A-Z_]+
 posix.SCHED_[A-Z_]+

tests/stubtest_allowlists/linux.txt

@@ -37,6 +37,9 @@ msvcrt
 winreg
 winsound
 
+# multiprocessing.popen_spawn_win32 exists on Linux but fail to import
+multiprocessing.popen_spawn_win32
+
 # Aliases for OSError
 posix.error.characters_written
 resource.error.characters_written