[CI Failure] Flaky: DashboardClientTests.SubscribeResources_ReplicaStartedAtChanged_EmitsParentChange sees duplicate resource change events

## Build Information

Build: https://github.com/microsoft/aspire/actions/runs/32293779852
Build error leg or test failing: Tests / Dashboard / Dashboard (ubuntu-latest) / `Aspire.Dashboard.Tests.Model.DashboardClientTests.SubscribeResources_ReplicaStartedAtChanged_EmitsParentChange`
Pull request: #19205

## Error Message

```
Assert.Single() Failure: The collection contained 2 matching items
Expected: (predicate expression)
Collection: [ResourceViewModelChange { ChangeType = Upsert, ... }, ...]
Match indices: 0, 3
at Aspire.Dashboard.Tests.Model.DashboardClientTests.SubscribeResources_ReplicaStartedAtChanged_EmitsParentChange()
```

## Description

Flaky: DashboardClientTests.SubscribeResources_ReplicaStartedAtChanged_EmitsParentChange sees duplicate resource change events

**Type**: flaky-test

## Occurrences

| Date | Build | Job | PR |
|------|-------|-----|----|
| 2026-08-19 | [32293779852](https://github.com/microsoft/aspire/actions/runs/32293779852) | Tests / Dashboard / Dashboard (ubuntu-latest) | #19205 |
| 2026-08-20 | [32375588350](https://github.com/microsoft/aspire/actions/runs/32375588350) | Tests / Hosting.Python / Hosting.Python (windows-latest) | #19335 |

Start by running Aspire.Dashboard.Tests.Model.DashboardClientTests.SubscribeResources_ReplicaStartedAtChanged_EmitsParentChange and review its resource subscription setup and the reported build logs. Reproduce the duplicate ResourceViewModelChange event if possible; done means the test reliably observes only the expected parent change and passes on the affected CI legs.

Written by the indexing model from the issue text.