Changing the frequency at which we update worktrees highlighted a
problem in the randomized tests that was causing clients to receive
a definition to a worktree *before* observing the registration of
the worktree itself. This was most likely caused by #1224 because
the scenario that pull request enabled was the following:
- Guest requests a definition pointing to a non-existant worktree
- Server forwards the request to the host
- Host sends an `UpdateProject` message
- Host sends a response to the definition request
- Server observes the `UpdateProject` message and tries to acquire
the store
- Given that we're waiting, the server goes ahead to process the
response for the definition request, responding *before*
`UpdateProject` is forwarded
- Server finally forwards `UpdateProject` to the guest
This commit ensures that, after forwarding a project request and getting a
response, we acquire a lock to the store again to ensure the project still
exists. This has the effect of ordering the forwarded request *after* any
message that was received prior to the response and for which we are still
waiting to acquire a lock to the store.