Change __main__ warning message from 'import' to 'preload'

For consistency with module preload warnings, use 'Failed to preload
__main__' instead of 'Failed to import __main__'.

Author: gpshead

Lib/multiprocessing/forkserver.py

@@ -247,7 +247,7 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None,
                         with warnings.catch_warnings():
                             warnings.simplefilter('always', ImportWarning)
                             warnings.warn(
-                                f"Failed to import __main__ from {main_path!r}: {e}",
+                                f"Failed to preload __main__ from {main_path!r}: {e}",
                                 ImportWarning,
                                 stacklevel=2
                             )