Test Failure: System.Net.WebSockets.Client.Tests.AbortTest_HttpClient_Loopback.Abort_SendAndAbort_Success

## Build Information
Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574201
Build error leg or test failing: System.Net.WebSockets.Client.Tests.AbortTest_HttpClient_Loopback.Abort_SendAndAbort_Success(useSsl: False)

## Error Message

Fill the error message using [step by step known issues guidance](https://github.com/dotnet/arcade/blob/main/Documentation/Build%20Analysis/KnownIssueJsonStepByStep.md).

```json
{
"ErrorPattern": "System\\.Net\\.WebSockets\\.Client\\.Tests\\.AbortTest_HttpClient_Loopback\\.Abort_SendAndAbort_Success.+\\[FAIL\\]",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574201
**Error message validated:** `[System\.Net\.WebSockets\.Client\.Tests\.AbortTest_HttpClient_Loopback\.Abort_SendAndAbort_Success.+\[FAIL\]`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 9/2/2026 9:58:14 PM UTC

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1574201](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574201)|dotnet/runtime|[System.Net.WebSockets.Client.Tests.AbortTest_HttpClient_Loopback.Abort_SendAndAbort_Success](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574201&view=ms.vss-test-web.build-test-results-tab&runId=43380118&resultId=203160)||
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|1|

Start with the linked build 1574201 and the failing test System.Net.WebSockets.Client.Tests.AbortTest_HttpClient_Loopback.Abort_SendAndAbort_Success(useSsl: False). Inspect the test failure details and reproduce the failure; done means identifying and addressing the cause so the test passes reliably.

Written by the indexing model from the issue text.