Add defer and inert to the list of boolean attributes

[marcospereira]

I noticed these two were missing, and they are now part of the list at https://meiert.com/en/blog/boolean-attributes-of-html/. The list removed a few attributes, but I kept them for the sake of compatibility.

Also, a small refactor to use Set.of. :-)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.31%. Comparing base (6a84710) to head (f07db26).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #356   +/-   ##
=========================================
  Coverage     91.31%   91.31%           
  Complexity     1218     1218           
=========================================
  Files            76       76           
  Lines          3168     3168           
  Branches        493      493           
=========================================
  Hits           2893     2893           
  Misses          164      164           
  Partials        111      111           

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[casid]

Thank you for keeping this up-to-date @marcospereira!