[CI Failure] Flaky: ProcessExecutionTests.WaitForExitAsync_WithGracefulServices_SignalerThrows_StillEscalatesToKill fails with 'Assert.Single() Failure: The collection was empty' on Windows

## Build Information

Build: https://github.com/microsoft/aspire/actions/runs/33494022725
Build error leg or test failing: Tests / Cli / Cli (windows-latest) / `Aspire.Cli.Tests.DotNet.ProcessExecutionTests.WaitForExitAsync_WithGracefulServices_SignalerThrows_StillEscalatesToKill`
Pull request: #19826

## Error Message

```
Assert.Single() Failure: The collection was empty
at Aspire.Cli.Tests.DotNet.ProcessExecutionTests.WaitForExitAsync_WithGracefulServices_SignalerThrows_StillEscalatesToKill(Boolean isolateConsole) in D:\a\aspire\aspire\tests\Aspire.Cli.Tests\DotNet\ProcessExecutionTests.cs:line 265
```

## Description

Flaky: ProcessExecutionTests.WaitForExitAsync_WithGracefulServices_SignalerThrows_StillEscalatesToKill fails with 'Assert.Single() Failure: The collection was empty' on Windows

**Type**: flaky-test

## Occurrences

| Date | Build | Job | PR |
|------|-------|-----|----|
| 2026-09-01 | [33494022725](https://github.com/microsoft/aspire/actions/runs/33494022725) | Tests / Cli / Cli (windows-latest) | #19826 |
| 2026-09-03 | [33782779276](https://github.com/microsoft/aspire/actions/runs/33782779276) | Tests / No-package tests (regular, Aspire.Hosting.CodeGeneration.TypeScript.Tests, Hosting.CodeGeneration... / Hosting.CodeGeneration.TypeScript (windows-latest) | #19465 |

Start with tests/Aspire.Cli.Tests/DotNet/ProcessExecutionTests.cs, especially line 265 and WaitForExitAsync_WithGracefulServices_SignalerThrows_StillEscalatesToKill. Run the targeted test on windows-latest, including both isolateConsole values, and compare the failing build runs. Done means the test reliably passes on Windows without the Assert.Single() collection-empty failure.

Written by the indexing model from the issue text.