Fix exception message expectation on MongoDB latest

[alcaeus]

On MongoDB latest, the error message is different as the validation is handled by the execution planner. The additional %S ensures that tests pass on upcoming versions of MongoDB as well.

[GromNaN]

What is the message in the new version?

[alcaeus]

The full error is:

Plan executor error during update :: caused by :: Document failed validation

Using %S we can still assert that the BulkWriteException was caused by a document validation failure, instead of having to remove the exception message entirely and only checking for a write exception that could be caused by multiple other things.

[GromNaN]

LGTM