E2E Deployment Test Failure: Aspire.Deployment.EndToEnd.Tests.AcaManagedRedisDeploymentTests.DeployStarterWithManagedRedisToAzureContainerApps

## Failing Test

`Aspire.Deployment.EndToEnd.Tests.AcaManagedRedisDeploymentTests.DeployStarterWithManagedRedisToAzureContainerApps`

## Symptom

The test fails consistently on nightly runs with:

```
04:42:07 (provision-cache) ✗ Failed to provision cache: Deployment failed:
Error code = OperationFailed, Message = The operation failed. (170.3s)
04:42:07 (provision-cache) ✗ [ERR] Step 'provision-cache' failed.
04:43:27 (pipeline-execution) ✗ [ERR] Deployment failed: Error code = OperationFailed, Message = The operation failed.
✅ 20/22 steps succeeded • ❌ 2 failed • Total time: 4m 16s
❌ Pipeline failed
```

## Root Cause

This appears to be an Azure-side failure when provisioning **Azure Managed Redis** in the test subscription/region. The deployment pipeline runs end-to-end and 20 of 22 steps succeed; only the `provision-cache` ARM/Bicep step is rejected by ARM after ~170 seconds with a generic `OperationFailed` error and no further detail surfaced by the pipeline.

This is not obviously a product or test bug — the test code, infrastructure, and pipeline all work; the Azure resource provider is rejecting the cache provisioning request.

## Next Steps

- Capture the underlying ARM deployment error from Azure (operation IDs, activity log) for one of the failing runs to determine whether this is:
- A regional capacity / SKU availability issue (try changing region or SKU).
- A subscription quota / policy issue.
- A regression in the generated Bicep for Managed Redis.
- Consider quarantining the test until the root cause is identified, given the consistent nightly failure.

## Affected Runs

- https://github.com/microsoft/aspire/actions/runs/26323258106 (2026-05-23)
- https://github.com/microsoft/aspire/actions/runs/26268417397 (2026-05-22)
- https://github.com/microsoft/aspire/actions/runs/26205530633 (2026-05-21)
- https://github.com/microsoft/aspire/actions/runs/26141293553 (2026-05-20)
- https://github.com/microsoft/aspire/actions/runs/26076159680 (2026-05-19)

> This issue was created automatically by a workflow analyzing Deployment E2E test failures on `main`. No fix PR has been opened because additional Azure-side investigation is needed before a high-confidence fix can be applied.