Update to matrix-sdk-crypto-wasm 15.1.0, and add new `ShieldStateCode.MismatchedSender` (#4916)
* test: add a flushPromises
this seems to be needed because `initRustCrypto` now ends up doing slightly
less awaiting
* Support new `ShieldStateCode.MismatchedSender`
* Update to matrix-sdk-crypto-wasm 15.1.0
* Add `waitFor` and use it instead of `flushPromises`
* minor lints and fixes
* another lint fix