hghave: update expected rustfmt version
We still use nightly, but have moved to a newer nightly after the last
CI image upgrade in
74f1bf147a6d and
3876d4c6c79e.
= Mercurial XXX =
== New Features ==
== Default Format Change ==
These changes affect newly created repositories (or new clones) done with
Mercurial XXX.
== New Experimental Features ==
== Bug Fixes ==
== Backwards Compatibility Changes ==
== Internal API Changes ==
== Miscellaneous ==