Reason
https://gerrit.wikimedia.org/r/admin/repos/phabricator/extensions/Sprint says Phabricator Sprint extension. Mirrored from https://phabricator.wikimedia.org/diffusion/PHSP/ and says State: Active.
However, https://phabricator.wikimedia.org/diffusion/PHSP/ says Publishing Disabled.

It is unmaintained, so I cannot add its maintainers to this task, but giving a heads-up to @mmodell if we share the same understanding.

To-do list

• This task
  • Add maintainers as subscribers to this task - not applicable
  • Add Phabricator project <#Phabricator-Sprint-extension> as a tag for this task
• On-wiki documentation
  • No related documentation page; updated https://www.mediawiki.org/w/index.php?title=Phabricator%2FCode&type=revision&diff=4418034&oldid=4379100
• Phabricator
  • Mark all Phabricator tasks for the extension/skin as Declined. Add a comment pointing to this task when doing so for reference.
  • Archive Phabricator project Phabricator-Sprint-Extension for the extension/skin.
  • Edit Phabricator project Phabricator-Sprint-Extension description for the extension/skin with a link to this ticket.
• Repositories
  • Empty repository in Gerrit, leaving only the README indicating the repo is archived, and referring to this task by URL.
  • Remove from phabricator/extensions / (along with in .gitmodules).
  • Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task): https://gerrit.wikimedia.org/r/admin/repos/phabricator/extensions/Sprint
  • Archive the Diffusion repository: https://phabricator.wikimedia.org/diffusion/PHSP/
  • Delete the GitHub mirror: https://github.com/wikimedia/phabricator-extensions-Sprint