gh-126631: gh-137996: fix pre-loading of `__main__`
The `main_path` parameter was renamed `init_main_from_name`, update the
forkserver code accordingly. This was leading to slower startup times when people
were trying to preload the main module.
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(cherry picked from commit 0912b3a6db)
Co-authored-by: Duane Griffin <duaneg@dghda.com>
