yes: deal with UnicodeDecodeError in input(), fixes #6984

[ThomasWaldmann]

if retry is True, it will just retry to get a valid answer. if retry is False, it will return the default.

the code can be tested by entering "error" (without the quotes).

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 81.82%. Comparing base (694fa93) to head (9d1107e).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
src/borg/helpers/yes_no.py	42.85%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8612      +/-   ##
==========================================
- Coverage   81.84%   81.82%   -0.03%     
==========================================
  Files          74       74              
  Lines       13311    13323      +12     
  Branches     1960     1963       +3     
==========================================
+ Hits        10894    10901       +7     
- Misses       1755     1758       +3     
- Partials      662      664       +2     

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