fix: Carousel does not start with CMS v4

[fsbraun]

When used with Django CMS 4+ the first carousel slide is not activated preventing the carousel from starting in the first place.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.93%. Comparing base (224506c) to head (6b3d89c).
Report is 139 commits behind head on master.

Files	Patch %	Lines
djangocms_frontend/helpers.py	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
- Coverage   86.28%   85.93%   -0.35%     
==========================================
  Files         110      110              
  Lines        2975     2980       +5     
  Branches      322      323       +1     
==========================================
- Hits         2567     2561       -6     
- Misses        310      318       +8     
- Partials       98      101       +3     

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