Flaky test: StartDetached_GrandchildSurvivesSignalingParent(enable: False)

## Build Information
Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1378923
Build error leg or test failing: System.Diagnostics.Tests.ProcessTests.StartDetached_GrandchildSurvivesSignalingParent
Pull request: https://github.com/dotnet/runtime/pull/126807

## Error Message

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.Diagnostics.Tests.ProcessTests.StartDetached_GrandchildSurvivesSignalingParent(enable: False)","Assert.Equal()"],
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

```
System.Diagnostics.Tests.ProcessTests.StartDetached_GrandchildSurvivesSignalingParent(enable: False) [FAIL]
Assert.Equal() Failure: Values differ
Expected: False
Actual: True
Stack Trace:
/_/src/libraries/System.Diagnostics.Process/tests/ProcessTests.cs(353,0): at System.Diagnostics.Tests.ProcessTests.StartDetached_GrandchildSurvivesSignalingParent(Boolean enable)
at InvokeStub_ProcessTests.StartDetached_GrandchildSurvivesSignalingParent(Object, Span`1)
/_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(95,0): at System.Reflection.MethodBaseInvoker.InvokeWithOneArg(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
```

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1378923
**Error message validated:** `[System.Diagnostics.Tests.ProcessTests.StartDetached_GrandchildSurvivesSignalingParent(enable: False) Assert.Equal()`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 4/15/2026 6:24:18 AM UTC

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