GHSA-JJ6P-3M75-G2P3 matrix-sdk-base denial of service via custom m.room.join_rules event values

The matrix-sdk-base crate is unable to handle responses that include custom m.room.joinrules values due to a serialization bug. This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventin...