bpo-12915: Fix test to recognize when filesystem encoding cannot encode Unicode string

[aixtools]

When filesystem encoding cannot encode the Unicode string used for a filename

continue testing with the next example.

https://bugs.python.org/issue12915

[codecov]

Codecov Report

Merging #18720 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18720      +/-   ##
==========================================
- Coverage   82.13%   82.13%   -0.01%     
==========================================
  Files        1955     1955              
  Lines      584601   584742     +141     
  Branches    44484    44488       +4     
==========================================
+ Hits       480156   480268     +112     
- Misses      94793    94825      +32     
+ Partials     9652     9649       -3     

Impacted Files	Coverage Δ
Lib/asynchat.py	80.00% <0.00%> (-2.07%)	⬇️
Modules/binascii.c	85.86% <0.00%> (-0.91%)	⬇️
Lib/ast.py	74.33% <0.00%> (-0.85%)	⬇️
Lib/test/test_poplib.py	92.80% <0.00%> (-0.80%)	⬇️
Lib/_weakrefset.py	59.18% <0.00%> (-0.69%)	⬇️
Lib/random.py	88.12% <0.00%> (-0.28%)	⬇️
Modules/expat/xmlparse.c	61.69% <0.00%> (-0.12%)	⬇️
Lib/asyncio/base_events.py	81.86% <0.00%> (-0.10%)	⬇️
Lib/functools.py	95.46% <0.00%> (ø)	⬆️
Objects/listobject.c	90.77% <0.00%> (ø)	⬆️
... and 14 more

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