MemoryCryptoStore.__init__() now requires account_id and pickle_key
positional arguments as of mautrix 0.21. The migration from matrix-nio
(commit 1850747) didn't account for this, causing E2EE initialization
to fail with:
MemoryCryptoStore.__init__() missing 2 required positional arguments:
'account_id' and 'pickle_key'
Pass self._user_id as account_id and derive pickle_key from the same
user_id:device_id pair already used for the on-disk HMAC signature.
Update the test stub to accept the new parameters.
Fixes#7803
050f496816