GitLab now uses a `/-/` component between the `group/project` part of
the URL and the `{issues,merge_requests,tree}` part so that it can
support `group/subgroup/project` with arbitrary depth.
Our practice of closing MRs temporarily while discussion
takes place in a separate issue isn't always well understood
by MR authors. Expiring a MR seems to be better understood,
but making it clear that it is also a temporary state is helpful.
The logic is that the describe output is readily available using `git
tag --contains` locally. In addition, for a hypothetical commit which
landed in both v3.9.4 and v3.10.1, there is no "better" tag to refer to.
since v3.10.0's relation to such a commit is unclear either way.
Also mention that a `Fixes` trailer is preferred if the mention is just
to indicate a commit which introduced an error rather than writing a
complete sentence about it.
