[CI Failure] Flaky: ExtensionChangelogFinalizedWorkflowTests.ReleaseBranchWithStaleExtensionBaseAdvanceFails fails on unrelated PRs, likely due to repo/branch state assumptions

## Build Information

Build: https://github.com/microsoft/aspire/actions/runs/33458228838
Build error leg or test failing: Tests / Infrastructure / Infrastructure (ubuntu-latest) / `Infrastructure.Tests.ExtensionChangelogFinalizedWorkflowTests.ReleaseBranchWithStaleExtensionBaseAdvanceFails`
Pull request: #15671

## Error Message

```
Assert.Contains() Failure: Sub-string not found
String: "::error file=extension/CHANGELOG.md,line=3,title=F"...
Not found: "Finalized changelog range ends at"
at Infrastructure.Tests.ExtensionChangelogFinalizedWorkflowTests.ReleaseBranchWithStaleExtensionBaseAdvanceFails() in /_/tests/Infrastructure.Tests/WorkflowScripts/ExtensionChangelogFinalizedWorkflowTests.cs:line 226
```

## Description

Flaky: ExtensionChangelogFinalizedWorkflowTests.ReleaseBranchWithStaleExtensionBaseAdvanceFails fails on unrelated PRs, likely due to repo/branch state assumptions

**Type**: flaky-test

## Occurrences

| Date | Build | Job | PR |
|------|-------|-----|----|
| 2026-09-01 | [33458228838](https://github.com/microsoft/aspire/actions/runs/33458228838) | Tests / Infrastructure / Infrastructure (ubuntu-latest) | #15671 |
| 2026-09-08 | [34251319766](https://github.com/microsoft/aspire/actions/runs/34251319766) | Tests / No-package tests / Hosting-4 (windows-latest) | #19678 |

Start with tests/Infrastructure.Tests/WorkflowScripts/ExtensionChangelogFinalizedWorkflowTests.cs, especially ReleaseBranchWithStaleExtensionBaseAdvanceFails() around line 226, and review the failing CI runs 33458228838 and 34251319766. Reproduce or compare the test on unrelated PRs to identify the repository or branch-state assumption. Done means the test reliably detects the stale extension-base case without failing on unrelated PRs.

Written by the indexing model from the issue text.