Fix invalidating OTK count cache after claim (#10875)

The invalidation was missing in `_claim_e2e_one_time_key_returning`,
which is used on SQLite 3.24+ and Postgres. This could break e2ee if
nothing else happened to invalidate the caches before the keys ran out.

Signed-off-by: Tulir Asokan <tulir@beeper.com>