Add test filename suffix

[jribbink]

Closes #1786

Description

Adds suffix to test files, was a bit of an oversight when I added this feature.

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Project coverage is 29.71%. Comparing base (3a6202f) to head (f52ba0c).

Files with missing lines	Patch %	Lines
internal/super/generate.go	0.00%	3 Missing ⚠️
internal/super/generator/test_template.go	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1785      +/-   ##
==========================================
+ Coverage   29.69%   29.71%   +0.01%     
==========================================
  Files          94       94              
  Lines        5182     5182              
==========================================
+ Hits         1539     1540       +1     
+ Misses       3463     3462       -1     
  Partials      180      180              

Flag	Coverage Δ
unittests	29.71% <69.23%> (+0.01%)	⬆️

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