Close locked MRs in MergeRequests::RefreshService

https://gitlab.zendesk.com/agent/tickets/84935

It looks like a Sidekiq job got picked by two hosts at once, which is scary (https://github.com/mperham/sidekiq/issues/3303).

I think the upshot of this was that the MR was merged, but we left it in a locked state. It was then unlocked automatically a couple of hours later, but by that time, it was marked as opened, even though it should be marked as merged.

In MergeRequests::RefreshService, we close MRs on a push to the target branch if the push to the target branch contains the MR's HEAD commit. We only do this for MRs in the opened state, though.

@oswaldo could we extend this to locked, perhaps by doing an additional check for the JID? That's not perfect, but it makes us less likely to fail in this way.