BEdita API and Core 5.29, cakephp 4.5

[didoda]

This updates composer.json dependencies to use BEdita 5.29, cakephp 4.5.
This also updates github workflow to run against php 8.3 too.
Bonuses:

• add dependabot.yml in github workflow, to automatically open PR for workflow related dependencies updates
• use codecov/codecov-action@v4 with CODECOV_TOKEN

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.1%. Comparing base (6d00b46) to head (981057c).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##             master     #15   +/-   ##
========================================
  Coverage      98.1%   98.1%           
  Complexity       69      69           
========================================
  Files             7       7           
  Lines           221     221           
========================================
  Hits            217     217           
  Misses            4       4           

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