Update to latest go-chi/session where the NewManager causes a new
Provider instantiation instead of reconfiguring an old one.
(https://gitea.com/go-chi/session/pulls/1)
The NewManager call is now concurrency safe and would allow live
reconfiguration in future but for now this PR simply fixes an
intermittent "data-race" detected in our tests. (See
https://drone.gitea.io/go-gitea/gitea/43900/2/14)
Related #17027
Related #1441
Signed-off-by: Andrew Thornton <art27@cantab.net>