Wait until the sync has stopped before marking a background task as complete.

[pixlwave]

Looking through some logs for #3478, there was an example where everything went wrong due to the task being marked as complete before the sync had stopped. Hopefully this should fix that issue.

[github-actions]

	Warnings
⚠️	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.

Generated by 🚫 Danger Swift against a96d2ca

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.

Project coverage is 78.58%. Comparing base (e70a95c) to head (a96d2ca).
Report is 6 commits behind head on develop.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
ElementX/Sources/Application/AppCoordinator.swift	0.00%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3564      +/-   ##
===========================================
- Coverage    78.61%   78.58%   -0.04%     
===========================================
  Files          757      757              
  Lines        63708    63713       +5     
===========================================
- Hits         50085    50066      -19     
- Misses       13623    13647      +24     

Flag	Coverage Δ
unittests	69.71% <0.00%> (+0.03%)	⬆️

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