Python UnicodeEncodeError in the unittest runner during uicheck on Windows

[Stephan Bergmann]

Trying to make uicheck work on Windows, I encountered a test failing due to

> FAIL: test_tdf125104_pageFormat_numbering (tdf125104.tdf125104)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "C:/lo/core/uitest/test_main.py", line 128, in <module>
>     result = unittest.TextTestRunner(stream=sys.stdout, verbosity=2).run(test_suite)
>   File "C:\lo\core\instdir\program\python-core-3.7.7\lib\unittest\runner.py", line 183, in run
>     result.printErrors()
>   File "C:\lo\core\instdir\program\python-core-3.7.7\lib\unittest\runner.py", line 110, in printErrors
>     self.printErrorList('FAIL', self.failures)
>   File "C:\lo\core\instdir\program\python-core-3.7.7\lib\unittest\runner.py", line 117, in printErrorList
>     self.stream.writeln("%s" % err)
>   File "C:\lo\core\instdir\program\python-core-3.7.7\lib\unittest\runner.py", line 25, in writeln
>     self.write(arg)
>   File "C:\lo\core\instdir\program\\python-core-3.7.7\lib\encodings\cp1252.py", line 19, in encode
>     return codecs.charmap_encode(input,self.errors,encoding_table)[0]
> UnicodeEncodeError: 'charmap' codec can't encode character '\u0916' in position 195: character maps to <undefined>

I assume the test itself fails due to some other reason, and then 
printing out that reason causes this error.  But I have no idea on which 
level to fix this.  Do we need to change something in the UITest 
machinery when we call that Python unittest runner, or is it a bug that 
needs patching in that Python unittest runner?