Clang-tidy fixes

[cbachhuber]

This PR fixes the clang-tidy issues in Option.hpp.

[codecov]

Codecov Report

Merging #360 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #360   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        3353   3354    +1     
=====================================
+ Hits         3353   3354    +1

Impacted Files	Coverage Δ
include/CLI/Validators.hpp	100% <ø> (ø)	⬆️
include/CLI/Option.hpp	100% <100%> (ø)	⬆️

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[henryiii]

The CI should be checking clang-tidy (though it might have been lost during the transition of formatting to GitHub Actions).

[phlptp]

I remember getting some PR's where the clang-tidy checks were triggered recently so I think it is still working, but I was also under the impression that was only checking a pretty limited subset of the clang-tidy checks and specifically ones where there was an auto fix that was possible.