Bump wxPython version to support newer python versions

I noticed that wxPython couldn't be installed as a dependency with
Python 3.12 on MacOS. It failed with the following error message:

ModuleNotFoundError: No module named 'attrdict'

After consulting wxWidgets/Phoenix#2296, I
found out that this was an issue with wxPython and confirmed that 4.2.1
works. I tested this locally.

requirements.txt

@@ -1,5 +1,5 @@
 wxPython>=4.0,<4.2.0 ; platform_system=="Linux" # See https://github.com/wxWidgets/Phoenix/issues/2225
-wxPython==4.2.0 ; platform_system!="Linux"
+wxPython==4.2.1 ; platform_system!="Linux"
 pyserial
 requests
 pywin32; platform_system=="Windows"