test: Add unit test for anonymous initial state access

[ChristophWurst]

This is a follow-up to #6115.

cc @am97

[ChristophWurst]

/backport to stable4.7

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 24.08%. Comparing base (60d03d4) to head (04db832).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6126   +/-   ##
=========================================
  Coverage     24.08%   24.08%           
  Complexity      457      457           
=========================================
  Files           247      247           
  Lines         11534    11534           
  Branches       2165     2165           
=========================================
  Hits           2778     2778           
  Misses         8441     8441           
  Partials        315      315           

Flag	Coverage Δ
javascript	15.56% <ø> (ø)
php	59.52% <ø> (ø)

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