Matplotlib 3.11.0 causes pcolormesh spatial plots to not show anything

### Describe the bug

## matplotlib 3.10.9

Plot looks normal.

## matplotlib 3.11.0

No spatial plot is shown, just the colourbar.

### How to reproduce

Steps to reproduce the behaviour:

0. Create a cset conda environment with matplotlib 3.11.0
1. `pytest -vvk test_spatial_pcolormesh_plot tests/operators/test_plot.py`
2. `display "$TMPDIR/pytest-of-$USER/pytest-current/test_spatial_pcolormesh_plotcurrent/plot.png"`
3. Observe breakage.

### Expected behaviour

Matplotlib 3.11 isn't meant to be a breaking change, so our plots should continue to work.

Start by running `pytest -vvk test_spatial_pcolormesh_plot tests/operators/test_plot.py` and inspect the spatial plotting code exercised by `test_spatial_pcolormesh_plot`. Compare the generated plot with Matplotlib 3.10.9 and 3.11.0 to identify the compatibility break. Done means the spatial plot renders again, including its data, and the targeted test passes.

Written by the indexing model from the issue text.