Fix /activity endpoint not require signature in authorized fetch mode (#15592)
Fix /activity endpoint not require signature in authorized fetch mode (#15592)

Fixes #15589

Co-authored-by: Claire <82b964c50e9d1d222e48cf5046e6484a966a7b07@sitedethib.com>
koba-lab/mastodon,koba-lab/mastodon,koba-lab/mastodon,koba-lab/mastodon