New versions of imagemagick fail to convert mass-ring.svg

[moorepants]

In #212 I encountered a failure due to imagemagick 7.1.1-47 not being about to process the mass-ring.svg file.

This is the error (seen if make SPHINXOPTS="--verbose" latexpdf" is used in the github action):

    Traceback (most recent call last):
      File "/home/runner/miniconda3/envs/test/lib/python3.12/site-packages/sphinx/ext/imgconverter.py", line 78, in convert
        subprocess.run(args, capture_output=True, check=True)
      File "/home/runner/miniconda3/envs/test/lib/python3.12/subprocess.py", line 571, in run
        raise CalledProcessError(retcode, process.args,
    subprocess.CalledProcessError: Command '['convert', '/home/runner/work/learn-multibody-dynamics/learn-multibody-dynamics/figures/mass-ring.svg[0]', _StrPath('/home/runner/work/learn-multibody-dynamics/learn-multibody-dynamics/_build/doctrees/images/mass-ring.png')]' returned non-zero exit status 1.

I tried a number of things in #212 but only reverting back to the imagemagick 7.1.1_36 from the last successful build in Nov 2025, did things start working. I should report a bug to imagemagick. I can also consider https://github.com/conda-forge/sphinxcontrib-svg2pdfconverter-feedstock as an alternative to imgconverter that ships with sphinx.