[Bug 57926] wine-mono wpfclipboard test can fail if a clipboard manager is running

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=57926

--- Comment #2 from Esme Povirk  ---
Actually, I don't think this is caused by the wpfclipboard test doing weird
things. This appears to be entirely contained in WPF's CriticalSetDataObject
method, which would mean it's not unlikely for this to happen in normal use.

And it seems WPF is making this more likely by inserting a 0.1 second Sleep
call between setting the clipboard and calling OleFlushClipboard. This makes it
even less likely that it's broken in this way on Windows.