fix(o11y): use correct Tokio task_local API in RequestRecorder

[haphungw]

RequestRecorder::current() was using RECORDER.try_get(), which is not a valid method on tokio::task::LocalKey, causing a compilation error.

Surfaced in #5292 when google_cloud_unstable_tracing is removed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.75%. Comparing base (10e89c0) to head (e0e0f65).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5293      +/-   ##
==========================================
- Coverage   97.75%   97.75%   -0.01%     
==========================================
  Files         215      215              
  Lines       44904    44904              
==========================================
- Hits        43897    43896       -1     
- Misses       1007     1008       +1     

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