Fix tick marker mirroring (matplotlib conversion)

[robertoffmoura]

Hi,

This fixes the issue where a matplotlib figure with only bottom and left tick markers would be converted to a plotly figure with markers on all sides.

Code PR

• I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the code generator and not the generated files.
• I have added tests or modified existing tests.
• For a new feature, I have added documentation examples (please see the doc checklist as well).
• I have added a CHANGELOG entry if changing anything substantial.
• For a new feature or a change in behavior, I have updated the relevant docstrings in the code.

[emilykl]

Hi @robertoffmoura, thank you for the fix! Same question here, could you provide some side-by-side comparisons to show the difference this PR introduces and why this is the correct behavior? I'm not very familiar with axis mirroring in matplotlib (or Plotly for that matter) so just trying to sanity check that these changes make sense.

I took a quick look at the images of the plots in the tests you added, and the only one where I see a difference between your branch and main is in the axis_mirror_false_with_one_sided_ticks function, is that expected?