UTDs on pinned messages are not retried after key is received

* Pinned message is recieved but cannot be decrypted
* key is downloaded from key backup
* no further attempt at redecrypting pinned message

Related to https://github.com/matrix-org/matrix-rust-sdk/issues/5474, and may well be fixed by https://github.com/matrix-org/matrix-rust-sdk/issues/3872