The WIP prefix toggling link on the sidebar only supported toggling
the *first* prefix specified in
`[repository.pullrequest].WORK_IN_PROGRESS_PREFIXES`. If the pull
request had a title with any other prefix, the first prefix listed in
the config was added (and then removed on toggling it off).
This little change makes all of the prefixes available for the
JavaScript function that does the toggling, and changes said function to
find the used prefix first, and toggle that.
When adding the prefix, it will still default to adding the first one
listed in the configuration, but it will happily remove any others if
those are present.
Fixes#3377.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
(cherry picked from commit a93a99eef3)
