Enhancement: Run infection on PHP 7.3

[localheinz]

This PR

• runs infection on PHP 7.3

[codecov]

Codecov Report

Merging #109 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #109   +/-   ##
=========================================
  Coverage     83.59%   83.59%           
  Complexity       91       91           
=========================================
  Files            14       14           
  Lines           317      317           
=========================================
  Hits            265      265           
  Misses           52       52

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