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 82.56%. Comparing base (2230932) to head (f056403).
Report is 24 commits behind head on 1.4-maint.

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

Additional details and impacted files

@@              Coverage Diff              @@
##           1.4-maint    #8597      +/-   ##
=============================================
+ Coverage      82.24%   82.56%   +0.31%     
=============================================
  Files             38       38              
  Lines          11076    11091      +15     
  Branches        2130     1716     -414     
=============================================
+ Hits            9110     9157      +47     
+ Misses          1390     1377      -13     
+ Partials         576      557      -19     

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