Correct naming of newly generated keyx files

[droidmonkey]

Fixes #6040

Testing strategy

Tested on Windows and macOS

Type of change

• ✅ Bug fix (non-breaking change that fixes an issue)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 63.68%. Comparing base (6c18b10) to head (acb12e7).
Report is 598 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/gui/databasekey/KeyFileEditWidget.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7010   +/-   ##
========================================
  Coverage    63.68%   63.68%           
========================================
  Files          330      330           
  Lines        41601    41601           
========================================
+ Hits         26491    26493    +2     
+ Misses       15110    15108    -2     

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