To do this we also update jinja-init to bullseye and gitea seems to be
the only user of this image. The impact of this should be fairly self
contained to gitea.
Note this update isn't urgent, but good hygiene. We should coordinate
this update with the 1.15.x gitea upgrade and do them in such a sequence
that we can identify problems easily if they pop up.
Change-Id: Ia0075416a1d8a067cfecd26c03f8db9641cbcb89
17ba858b19