I18N: Move the support forums URL in update-related HTTP API error messages to...

I18N: Move the support forums URL in update-related HTTP API error messages to a separate translatable string that is already used elsewhere.

Props ramiy, SergeyBiryukov.
Fixes #38880.
Built from https://develop.svn.wordpress.org/trunk@39325


git-svn-id: https://core.svn.wordpress.org/trunk@39265 1a063a9b-81f0-0310-95a4-ce76da25c4cd