Use labkit 96e583c57891

This change updates our labkit dependency to change logging behavior. There is only one change: labkit!53 (merged)

Prior version of labkit incorrectly logged HTTP status code 0 for some responses with an empty body. This labkit version will log 200 instead, which is also what the client sees.

This is part of gitlab-com/gl-infra/scalability#332 (closed)