Add -Wsign-conversion to the list of common warning flags

[Wmbat]

Description

Fixes all implicit sign conversions and turns on -Wsign-conversion when building catch2. I usually tried to find a good solution to the warning instead of casting.

Ran all the tests on my machine and it seemed good to go

GitHub Issues

Related to #2583

[codecov[bot]]

Codecov Report

Merging #2775 (f28ab91) into devel (0520ff4) will decrease coverage by 0.06%. The diff coverage is 75.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #2775      +/-   ##
==========================================
- Coverage   91.45%   91.39%   -0.06%     
==========================================
  Files         194      194              
  Lines        8197     8196       -1     
==========================================
- Hits         7496     7490       -6     
- Misses        701      706       +5