Re: [PATCH 4/4] ci/test-documentation: work around SyntaxWarning in Python 3.12

Patrick Steinhardt [off-list ref] writes:

These escape sequences seem to be part of Asciidoc itself. In the long
term, we should probably consider dropping support for Asciidoc in favor
of Asciidoctor. Upstream also considers itself to be legacy software and
recommends to move away from it [2]:
...
For now though, let's expand its lifetime a little bit more by filtering
out these new warnings. We should probably reconsider once the warnings
are upgraded to errors by Python.

Sounds sensible.  We can throw it in to the Git 3.0 list, perhaps
;-)