wx Custom Button Editor DisplayedText Query not working?

Currently a test is failing on wx:
```
======================================================================
FAIL: test_custom_button_editor (traitsui.tests.editors.test_button_editor.TestButtonEditor)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/aayres/Desktop/traitsui/traitsui/tests/editors/test_button_editor.py", line 112, in test_custom_button_editor
self.check_button_text_update(custom_view)
File "/Users/aayres/Desktop/traitsui/traitsui/tests/editors/test_button_editor.py", line 96, in check_button_text_update
self.assertEqual(actual, "I'm a play button")
AssertionError: '' != "I'm a play button"
+ I'm a play button

----------------------------------------------------------------------
```

The relevant code for DisplayedText in UITester is here:
https://github.com/enthought/traitsui/blob/f7fa4b48d2223d60e1e3327bda2bf7501b0fba8e/traitsui/testing/tester/_ui_tester_registry/wx/_traitsui/button_editor.py#L78-L82
printing the control in the test, I see that with custom style it is ``, and with simple ``. wx Windows do have a `GetLabel` method as well, but for some reason this is giving `""` here, as opposed to "I'm a play button".

Calling `configure_traits in the test on wx gives:

So it does appear that the displayed text is correct. Hence my suspicion this issue stems from UITester.

Current plan is to skip the test on. wx for now and leave this issue open as I am currently trying to clean up wx CI.