Fix flaky tornado test by increasing delta tolerance to 0.02 (#4550)

* Initial plan

* Fix flaky tornado test by increasing delta tolerance to 0.02

The test_metrics_concurrent_requests test was flaky on pypy/ubuntu
because the delta between server and client duration for fast async
requests can exceed 0.01 seconds due to scheduling jitter.

Assisted-by: Claude Sonnet 4

Agent-Logs-Url: https://github.com/open-telemetry/opentelemetry-python-contrib/sessions/a65606a0-612d-49b2-bcda-8b3942ee3e63

Co-authored-by: xrmx <12932+xrmx@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: xrmx <12932+xrmx@users.noreply.github.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>