graphviz: 2.40.1 -> 2.42.2

Little uncertain what's going on re:versions,
here's some info:

2.42.0 "Fixes quite a few bugs"[1], which is primary motivation.

[1] https://gitlab.com/graphviz/graphviz/blob/stable_release_2.42.0/ChangeLog

2.42.1 has a note in 2.42.2's ChangeLog[2] which is good but also
interesting as 2.42.2 doesn't have an entry in its own ChangeLog :).
FWIW there are two tags for 2.42.2 but happily they're equivalent.

While a bit verbose, the changes between these versions can be looked at
using git locally or a URL like one of these:

* https://gitlab.com/graphviz/graphviz/compare/stable_release_2.42.0...stable_release_2.42.2
* https://gitlab.com/graphviz/graphviz/compare/stable_release_2.40.1...stable_release_2.42.0

Anyway, looks like a bunch of bugfixes! :)