Flaky test RegexMatchTests.Match_TestThatTimeoutHappens(engine: SourceGenerated)

## Build Information
Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1420477
Build error leg or test failing: System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
Pull request: https://github.com/dotnet/runtime/pull/128072

## Error Message

**DO NOT USE JSON BELOW IF THIS IS A BUILD BREAK** otherwise build analysis will allow pull requests to merge that break the build worse. For a build break, do not use this issue form. Make a regular new issue.

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

```json
{
"ErrorMessage": "System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: SourceGenerated) [FAIL]",
"BuildRetry": true,
"ExcludeConsoleLog": false
}
```

Previous issues about this test: https://github.com/dotnet/runtime/issues/117111, https://github.com/dotnet/runtime/issues/106096, https://github.com/dotnet/runtime/issues/88418

```
System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: SourceGenerated) [FAIL]
Assert.Throws() Failure: No exception was thrown
Expected: typeof(System.Text.RegularExpressions.RegexMatchTimeoutException)
Stack Trace:
/_/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs(1600,0): at System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(RegexEngine engine)
--- End of stack trace from previous location ---
--- End of stack trace from previous location ---
```

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1420477
**Error message validated:** `[System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: SourceGenerated) [FAIL]`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 5/14/2026 3:03:26 PM UTC

### Report
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|0|