Follows-up 0e9aa90 which introduced MAX_BODY_LENGTH,
and fec6bd9 which removed it again due to being too low for static
site deployments where small changes often change all files and thus
produce fairly large GitHub Push eventsm because they are essentially
a JSON wrapper around `git show` with a full file listing.

GitHub Docs promise to limit the 'added', 'removed', and 'changed'
arrays to 5000 file paths each (if more, the array is capped, in favor
of recommending you call their API for the full details instead), or
25 MB overall (event is dropped by them if still larger than that).

Note that we don't need any of this information, but there's no way
to opt-out of this afaik.

Note that we did not actually remove the limit in that patch in
practice, because we run it with Nginx in front, and that limits the
request body to 1MiB. That has been large enough so reflect that in
the Node.js service directly as well, to benefit other potential users
of the package.

Credit to Quarkslab for the discovery and recommended mitigation.

Ref jquery/infrastructure#565.