PyProgress is broken in demo

[Correct-Syntax]

Operating system: Windows 10, 64-bit
wxPython version & source: wxpython extras wheel, 4.1.1
Python version & source: python 3.9, from python.org

Description of the problem:

In the wxpython demo, the pyprogress is broken with the below error:

Error message (click to expand)

Traceback (most recent call last):
  File "agw\PyProgress.py", line 107, in OnStartProgress
    dlg = PP.PyProgress(None, -1, "PyProgress Example",
  File "C:\Python39\lib\site-packages\wx\lib\agw\pyprogress.py", line 495, in __init__
    buttonSizer.Add(self._btnAbort, 0, sizerFlags, LAYOUT_MARGIN)
wx._core.wxAssertionError: C++ assertion "!(flags & wxALIGN_RIGHT)" failed at ..\..\src\common\sizer.cpp(2168) in wxBoxSizer::DoInsert(): Horizontal alignment flags are ignored in horizontal sizers

[swt2c]

Thanks, PR submitted.