[release/8.0] Fix Dispose and SendData Race on Http3 Test

[github-actions]

Backport of #91291 to release/8.0

Fixes#87552

/cc @liveans

Customer Impact

Test only change to decrease noise in CI.
Fixes test System.Net.Http.Functional.Tests.HttpClientHandlerTest_Http3.ServerSendsTrailingHeaders_Success, which failed 3x per day (but passed on rerun).

Testing

CI in main had no hits in 2 days - previously failed 3x per day.

Risk

No risk, the test only change

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Issue Details

---

Backport of #91291 to release/8.0

/cc @liveans

Customer Impact

Testing

Risk

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

• If the change touches code that ships in a NuGet package, you have added the necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-System.Net.Http
Milestone:	-

[liveans]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[liveans]

Failures are unrelated to this PR.
Mostly related to #91705 and the rest of them are also unrelated.

Failures (updated by @karelz):

• Build android-x64 Release AllSubsets_Mono_RuntimeTests_Interp monointerpreter - Console log
  • Error: Failed to install mobile app.
• Networking certificate test failures #91705
  • Build iossimulator-x64 Release AllSubsets_Mono
  • Build maccatalyst-x64 Release AllSubsets_Mono
  • Build osx-x64 Release NativeAOT_Libs
  • Build tvos-arm64 Release AllSubsets_Mono
  • Build tvos-arm64 Release AllSubsets_NativeAOT
• Build iossimulator-x64 Release AllSubsets_Mono_RuntimeTests - Console log
  • Error: Failed to get ExitCode: System.InvalidOperationException: Process must exit before requested information can be determined.
• Build linux-arm64 Release NativeAOT_Libs - Console log
  • Error:
    • [FAIL] System.Net.Http.Functional.Tests.SocketsHttpHandlerTest_Http2.Http2_IncorrectServerPreface_RequestFailsWithAppropriateHttpProtocolException
    • Assert.Equal() Failure
    • Expected: HttpProtocolError
    • Actual: Unknown
• Build linux-x64 Release NativeAOT_Libs
  • Error: Exit code 137 returned from process: file name '/usr/bin/docker', arguments 'exec -i -u 1000 -w /home/cloudtest_azpcontainer e563c68b5e718e4aafc16f965038ddbc1744ed9fd3b21fb491217131ca537fe3 /__a/externals/node/bin/node /__w/_temp/containerHandlerInvoker.js'.
• Build tvos-arm64 Release AllSubsets_NativeAOT_RuntimeTests - Console log
  • Error:
    • nativeaot/SmokeTests/StackTraceMetadata/StackTraceMetadata/StackTraceMetadata.sh [FAIL]
    • Expected: True
    • Actual: False
    • Stack Trace: at nativeaot_SmokeTests_StackTraceMetadata.StackTraceMetadata_StackTraceMetadata._StackTraceMetadata_StackTraceMetadata_sh()
• Build tvossimulator-x64 Release AllSubsets_Mono_RuntimeTests - Console log - Unclear error

Rerunning the failures

[karelz]

Test only change, I approve - @artl93 ready for your approval

[artl93]

M2 approved.

[karelz]

Adding Servicing-Approved label per @artl93's approval above.

[artl93]

Adding Servicing-Approved label per @artl93's approval above.

Yes, thank you!