Bump Sentry Android to 6.0.0-beta.4

[ueman]

📜 Description

Bump Sentry Android to 6.0.0-beta.4

💡 Motivation and Context

This is the prerequisite for #847

💚 How did you test it?

This is covered by existing tests.

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

Test & merge #847

[codecov-commenter]

Codecov Report

Merging #871 (9852532) into main (188f470) will decrease coverage by 0.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #871      +/-   ##
==========================================
- Coverage   90.33%   89.94%   -0.39%     
==========================================
  Files         119        9     -110     
  Lines        3785      169    -3616     
==========================================
- Hits         3419      152    -3267     
+ Misses        366       17     -349     

Impacted Files	Coverage Δ
dart/lib/src/protocol/sentry_thread.dart
...lib/src/environment/_io_environment_variables.dart
dart/lib/src/sentry_envelope_item_header.dart
dart/lib/src/protocol/sentry_transaction.dart
...rc/client_reports/noop_client_report_recorder.dart
...src/integrations/native_app_start_integration.dart
dart/lib/src/sentry_sampling_context.dart
dart/lib/src/protocol/debug_image.dart
dart/lib/src/platform/_io_platform.dart
dart/lib/src/sentry_span_context.dart
... and 100 more

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