Fix: Drop support for PHP 7.3

[localheinz]

This pull request

• drops support for PHP 7.3

[codecov]

Codecov Report

Merging #157 (d89d105) into main (da97c60) will not change coverage.
The diff coverage is n/a.

❗ Current head d89d105 differs from pull request most recent head 83f468b. Consider uploading reports for the commit 83f468b to get more accurate results

@@             Coverage Diff             @@
##                main      #157   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        12        12           
===========================================
  Files              3         3           
  Lines             39        39           
===========================================
  Hits              39        39           

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