fix(Telemetry): Improve baggage relay tests

[emyller]

Contributes [indirectly] to https://github.com/Flagsmith/flagsmith-private/issues/152

Improve test coverage of W3C Baggage relaying behaviour by ensuring that:

• OTel's baggage.get_baggage() consumes baggage from Django requests
• Baggage is echoed in logs emitted in the request span

[gemini-code-assist]

Code Review

This pull request adds integration tests to verify that baggage headers in Django requests are correctly extracted to the OpenTelemetry context and propagated to log attributes. The feedback suggests wrapping the context attachment and detachment in a try...finally block to prevent test pollution in case of failures.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (3ed4d29) to head (7aa35fe).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #231      +/-   ##
==========================================
+ Coverage   97.39%   97.40%   +0.01%     
==========================================
  Files         105      105              
  Lines        4600     4618      +18     
==========================================
+ Hits         4480     4498      +18     
  Misses        120      120              

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