Posthog: use correct API for user properties

[BillCarsonFr]

Follow up on #2788

Posthog SDK has now an API to pass user properties, so no need to manually add them as $set in the event properties.
Updated the tests

Pull Request Checklist

• I read the contributing guide
• Pull request contains a changelog file in ./changelog.d
• Pull request includes a sign off

UI changes have been tested with:

• iPhone and iPad simulators in portrait and landscape orientations.
• Dark mode enabled and disabled.
• Various sizes of dynamic type.
• Voiceover enabled.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

	Warnings
⚠️	Please add a changelog.
⚠️	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.
⚠️	Please add a sign-off to either the PR description or to the commits themselves.

Generated by 🚫 Danger Swift against 964b45d

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.30%. Comparing base (6ca92c2) to head (964b45d).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2793      +/-   ##
===========================================
- Coverage    73.35%   73.30%   -0.05%     
===========================================
  Files          597      597              
  Lines        42703    42694       -9     
===========================================
- Hits         31323    31296      -27     
- Misses       11380    11398      +18     

Flag	Coverage Δ
unittests	62.22% <100.00%> (-0.06%)	⬇️

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