build failure: DeprecationWarning during docutils dependency install

[jayaddison]

Describe the bug

The continuous integration unit test workflow uses an environment variable to treat most warnings as errors by default.

Recently, pip has begun emitting a DeprecationWarning during the installation of docutils on versions of Python below 3.12, resulting in build failures.

I think that this may be related to pypa/pip#11916, where the version of setuptools vendored by pip was updated (and the relevant warning was introduced).

Overriding that particular warning message (while continuing to treat other warnings as errors) may be the safest and simplest way forward; I'll provide a pull request to do that.

How to Reproduce

I think that any continuous integration builds for this repository that utilise pip 23.1 are likely to be affected.

When opening a pull request to include the fix, I'll begin with something like a no-op commit to demonstrate the expected build failure, and after that a subsequent commit containing the fix (and hopefully illustrating that the build passes with that in place).

Environment Information

N/A

Sphinx extensions

N/A

Additional context

No response