wcsaxes tests fail with "The collections attribute was deprecated in Matplotlib 3.8"

[pllim]

devdeps job is failing for 5 tests with this message:

Matplotlib: 3.8.0.dev1437+g3b3fc57f65

matplotlib._api.deprecation.MatplotlibDeprecationWarning:
The collections attribute was deprecated in Matplotlib 3.8 and
will be removed two minor releases later.

• astropy/visualization/wcsaxes/tests/test_misc.py::test_no_numpy_warnings[contours]
• astropy/visualization/wcsaxes/tests/test_misc.py::test_grid_type_contours_transform
• astropy/visualization/wcsaxes/tests/test_misc.py::test_contour_return
• astropy/visualization/wcsaxes/tests/test_misc.py::test_contour_empty
• astropy/visualization/wcsaxes/tests/test_misc.py::test_multiple_draws_grid_contours

astropy/astropy/visualization/wcsaxes/coordinate_helpers.py

Line 621 in edf7493

for line in self._grid.collections:

astropy/astropy/visualization/wcsaxes/coordinate_helpers.py

Line 1126 in edf7493

for line in self._grid.collections:

Any ideas how to fix? @astrofrog @Cadair @dstansby @ayshih 🙏

Probably from matplotlib/matplotlib#25247

[dstansby]

Is there a longer stack trace for the error than posted above? (where perhaps it's easier to see where the warning is coming from)

[dstansby]

If it's a ContourSet emitting these, https://github.com/matplotlib/matplotlib/pull/25247/files#diff-918125f8b0a3d8085b15096d948f8e005d5dc938ea54501ba3c1f7a36ad74f7f is the MPL changelog entry that has info on how to change code to adapt to this.

[pllim]

That change log isn't very helpful for me who is unfamiliar with the code base, but I think I found the PR so looking at their diff, I am trying out #15004 🤞