bug: TypeError: '<' not supported between instances of 'NoneType' and 'int' when rendering source

[pawamoy]

Description of the bug

If a Griffe object has its lineno attribute set to None, rendering its source will fail.

To Reproduce

Add a Griffe extension that adds a member, created manually (in the extension) without a lineno.
Render it in the docs. Enable show_source: true.

Full traceback

Full traceback

  File "/home/pawamoy/data/dev/qtile/.venv/lib/python3.12/site-packages/mkdocstrings_handlers/python/templates/material/_base/function.html", line 99, in block 'source'
    {{ function.source|highlight(language="python", linestart=function.lineno, linenums=True) }}
^^^^^^^^^^^^^^^^^
  File "/home/pawamoy/data/dev/qtile/.venv/lib/python3.12/site-packages/mkdocstrings/handlers/rendering.py", line 120, in highlight
    result = super().highlight(src, language, inline=inline, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/pawamoy/data/dev/qtile/.venv/lib/python3.12/site-packages/pymdownx/highlight.py", line 385, in highlight
    if not linenums or linestart < 1:
                       ^^^^^^^^^^^^^
TypeError: '<' not supported between instances of 'NoneType' and 'int'

Expected behavior

Rendering the source shouldn't make MkDocs crash, even if lineno is None.

Environment information

python -m mkdocstrings_handlers.python.debug  # | xclip -selection clipboard

• System: Linux-6.8.9-arch1-2-x86_64-with-glibc2.39
• Python: cpython 3.12.1 (/home/pawamoy/data/dev/qtile/.venv/bin/python)
• Environment variables:
  • PYTHONPATH: /home/pawamoy/.local/pipx/venvs/pdm/lib/python3.11/site-packages/pdm/pep582
• Installed packages:
  • mkdocs v1.6.0
  • mkdocstrings v0.25.1
  • mkdocstrings-python v1.10.0.1.8.1
  • griffe v0.45.0

Additional context

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