[Bug 55417] New: user32:msg - test_showwindow() sometimes fails due to an unexpected WM_SYNCPAINT message on Windows 10

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=55417

Bug ID: 55417
           Summary: user32:msg - test_showwindow() sometimes fails due to
                    an unexpected WM_SYNCPAINT message on Windows 10
           Product: Wine
           Version: unspecified
          Hardware: x86-64
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: user32
          Assignee: [e-mail]
          Reporter: [e-mail]

user32:msg - test_showwindow() sometimes fails due to an unexpected
WM_SYNCPAINT message on Windows 10:

msg.c:5016: Test failed: ShowWindow(SW_SHOWNA) on visible top level window: 0:
the msg 0x0018 was expected, but got msg 0x0088 instead
msg.c:5016: Test failed: ShowWindow(SW_SHOWNA) on visible top level window: 1:
the msg 0x0046 was expected, but got msg 0x0018 instead
msg.c:5016: Test failed: ShowWindow(SW_SHOWNA) on visible top level window: 6:
the msg sequence is not complete: expected 0000 - actual 0046

See https://test.winehq.org/data/patterns.html#user32:msg

Where: 0x18 == WM_SHOWWINDOW
       0x46 == WM_WINDOWPOSCHANGING
       0x88 == WM_SYNCPAINT

Maybe the WM_SYNCPAINT should just be added as optional.

This only happened 4 times in the past 8 months:
* 2022-12-09 win21H1_newtb-w10pro64-zh-CN-64
* 2023-03-27 win21H1_newtb-w10pro64-ko-64
* 2023-06-09 win21H1_newtb-w10pro64-ja-64
* 2023-08-04 win21H1_newtb-w10pro64-ja-64