.NET: Stabilize steering harness session reuse test

[rogerbarreto]

Summary

Investigate and stabilize the steering harness test
SteerableLongRunningIntegrationTests.ActiveMafTurn_QueuesSteeringThenRunsItOnTheSameSessionAsync.
It has failed repeatedly in the .NET CI suite while earlier runs passed. The root cause
is not yet established; determine whether this is a test synchronization problem or a
runtime behavior regression rather than assuming the assertion is wrong.

Affected test

dotnet/tests/Microsoft.Agents.AI.Foundry.Hosting.UnitTests/SteerableLongRunningIntegrationTests.cs

The assertion immediately after submitting a steering request expects
agent.RunCount == 1, but CI observes 2. The test subsequently verifies sequential
execution and reuse of the same session.

CI evidence

Environment: net10.0, ubuntu-latest, Release.

• https://github.com/microsoft/agent-framework/actions/runs/34848588032/job/103990942953
• https://github.com/microsoft/agent-framework/actions/runs/34870463355/job/104065211461

Both runs report Assert.Equal() Failure: Values differ, expected 1, actual 2,
at SteerableLongRunningIntegrationTests.cs:57. The second failure persisted after
the branch update in #8263.

Temporary mitigation

Temporarily skip only this test using the repository's existing xUnit skip convention,
with the skip reason linking to this tracking issue. Preserve its body and assertions.
Do not disable the test class, project, CI workflow, or other tests.

The temporary skip is not the final fix. Keep this issue open after that change.

Resolution criteria

• Reproduce and identify the cause under relevant CI scheduling/parallelism conditions.
• Fix the test synchronization or runtime behavior as appropriate, without weakening
  the intended sequential-execution and session-continuity guarantees.
• Remove the temporary skip and demonstrate repeated passing execution of the test
  and the affected suite.

[rogerbarreto]

@copilot Please open a focused PR against main to temporarily skip only SteerableLongRunningIntegrationTests.ActiveMafTurn_QueuesSteeringThenRunsItOnTheSameSessionAsync in dotnet/tests/Microsoft.Agents.AI.Foundry.Hosting.UnitTests/SteerableLongRunningIntegrationTests.cs. Use the existing xUnit [Fact(Skip = "...")] convention with a clear temporary reason and a link to #8376. Preserve the test body and all assertions; do not change production code or disable other tests, the project, or CI workflows. Run the affected project checks and verify only this test is newly skipped. This is an interim mitigation: reference this issue without a closing keyword and leave it open for root-cause investigation and re-enabling the test.