WikiCloth patch: Switch MD5 to SHA256

In https://gitlab.com/gitlab-org/gitlab/blob/6c03aad1d81c574b695b207eb4335d6905f24ba5/config/initializers/wikicloth_redos_patch.rb#L113, it appears we patch WikiCloth, which uses MD5 as a digest.

In FIPS mode (Gitlab::FIPS.enabled?), we must eliminate the use of MD5 in favor of SHA256.

Can this be switched safely (and upstream)?

/cc: @cwoolley-gitlab

Testing

Regression testing required, please ensure all tests still pass after the chosen implementation.