Add basic dependabot config to update GHA

[ockham]

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[github-actions]

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Props bernhard-reiter.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.51%. Comparing base (818c12a) to head (662bf3e).
⚠️ Report is 2 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #375      +/-   ##
============================================
- Coverage     54.11%   52.51%   -1.60%     
  Complexity     4419     4419              
============================================
  Files           298      298              
  Lines         39448    39448              
============================================
- Hits          21348    20718     -630     
- Misses        18100    18730     +630     

Flag	Coverage Δ
e2e-js	45.71% <ø> (-0.02%)	⬇️
e2e-php	40.19% <ø> (-2.64%)	⬇️
javascript	15.07% <ø> (ø)
phpunit	29.96% <ø> (ø)

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