Fix: Drop support for PHP 7.3

[localheinz]

This pull request

• drops support for PHP 7.3

[codecov]

Codecov Report

Merging #540 (ceec149) into main (77d1b30) will not change coverage.
The diff coverage is n/a.

❗ Current head ceec149 differs from pull request most recent head 41b3145. Consider uploading reports for the commit 41b3145 to get more accurate results

@@             Coverage Diff             @@
##                main      #540   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        87        87           
===========================================
  Files             12        12           
  Lines            302       302           
===========================================
  Hits             302       302           

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