Return type of update() is incorrect

In the current version of Monk, `v7.3.3` the return type of `update()` is `UpdateWriteOpResult`, I think it should be `UpdateResult`.

https://github.com/Automattic/monk/blob/027ab439726d3ce87553c76caf777de32db5b12c/index.d.ts#L335-L339

(Same with the other `update()` calls, perhaps?)

Open index.d.ts at lines 335-339 and inspect the return type declared for update(). Check the other update() declarations mentioned in the issue, then confirm that each uses UpdateResult rather than UpdateWriteOpResult; done means the declarations consistently expose the intended return type.

Written by the indexing model from the issue text.