MNT: Stick with wxpy 4.0.7
We are still not able to upgrade beyond wxpython 4.0.7:
- wxpython 4.1.0 does not work on macOS (https://github.com/conda-forge/wxpython-feedstock/issues/70)
- wxpython 4.1.1 does not work with XQuartz (https://github.com/wxWidgets/Phoenix/issues/1923)