(Website issue) link to bugtracker is outdated

Dear developers,

this is not a problem in spice itself but a problem with your website at https://www.spice-space.org/developers.html. I just found no better bugtracker for this, so I hope this is okay.

Specifically, the issue is that that website still links to the old bugtrackers at https://bugs.freedesktop.org/enter_bug.cgi?product=Spice, which seems to be no longer active. It should likely link to somewhere in this GitLab instead.