Bug#1064575: python-pyswarms-doc: please make the build reproducible.

[James Addison]

Followup-For: Bug #1064575

On Sat, 24 Feb 2024 12:33:50 +0000, I wrote:
> Part of the documentation rendering process - I have not determined exactly
> what yet - adds an 'alt' attribute when it does not exist, and generates a
> randomized hex string to use as the value of the attribute.  This causes the
> resulting python-pyswarms-doc package to vary on each build.

Part of the reason for this appears to be the nbsphinx component; when it
encounters HTML <img> elements, it emits reStructuredText markdown containing
an alt attribute if one was found on the element, and defines an rST
substitution[1] named by a UUID4-generated value converted to hexadecimal.

Next question: where is that substitution name used when the ':alt:' option
is not found on the image directive?

[1] - https://sources.debian.org/src/nbsphinx/0.8.11%2Bds-1/src/nbsphinx.py/#L1398-L1399