Fix Hierarchical tracing test broken by ForceDefaultIdFormat

[MihaZupan]

Fixes #3020

Copilot's description:

Microsoft.Testing.Extensions.Telemetry (part of the test runner) brings
in Microsoft.ApplicationInsights/2.23.0, which sets
Activity.ForceDefaultIdFormat = true globally.  This forces all new
Activities to use W3C format regardless of the parent activity's format,
causing the Hierarchical test case to emit traceparent/tracestate
headers instead of the expected Request-Id header.

Introduced in #2940