[CI] iOS 16 simulator runtime downloads fail with connection reset by peer

## Failure signature

During `Provision system dependencies`, the required iOS 16.0 simulator is unavailable through `xcodebuild`, so provisioning falls back to Apple's downloadable simulator index. The runtime download then fails with:

```text
curl: (56) Recv failure: Connection reset by peer
Failed to download the iOS 16.0 simulator runtime.
The iOS 16.0 simulator is not installed, and it couldn't be downloaded.
```

## Confirmed occurrences

| PR / head | Build attempt / job | Worker |
|---|---|---|
| #26274 / `c6514d837dbf5f878369ed1176979040e1d2ab93` | [14753211 attempt 1 - dotnettests_ios / Provision system dependencies](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=14753211&view=logs&j=8cda949e-c02b-5944-aa3c-d0414112a761&t=c47ecfc2-ff0b-5dc2-2b9e-f595580d9a83) | `AcesShared 61` |
| #26274 / `c6514d837dbf5f878369ed1176979040e1d2ab93` | [14753211 attempt 1 - monotouch_maccatalyst / Provision system dependencies](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=14753211&view=logs&j=73408371-a55e-5ff5-5372-c49d56cfe7c2&t=468ca8b0-24e1-5c81-b8ff-f959535b008f) | `AcesShared 73` |
| #26279 / `84d989d3c2e6b0423d061fa59431d104157c895d` | [14753669 attempt 1 - interdependent-binding-projects / Provision system dependencies](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=14753669&view=logs&j=423b2900-bf2a-55b5-1a4f-b15b829a55ad&t=442ac673-4ff8-5c5f-39e1-2adfbf70c554) | `AcesShared 103` |

**Total:** 3 jobs across 2 distinct monitored PRs.

First observed: 2026-07-24 00:07 UTC. Latest observed: 2026-07-24 01:04 UTC.

## Classification and impact

This is a CI infrastructure/network failure, not a source build or test failure:

- It reproduces on unrelated PRs and three different workers.
- The failure occurs before repository tests start.
- Later missing TestSummary, HtmlReport, and drop artifacts are cascading errors caused by provisioning not completing.

## Investigation performed

- Inspected each Azure timeline and selected the first failed task in each job.
- Verified the exact simulator asset and normalized curl error in the provisioning task logs.
- Searched all open and closed `dotnet/macios` issues using the exact exception, simulator runtime name, task name, and downloadable-index fallback; no matching issue existed.
- Kept this separate from Xcode archive transport failures because the affected asset and provisioning phase differ.

## Retry status and workaround

Both affected builds are still active, so no retry has been submitted. Once each run is terminal, refresh the PR head and mergeability, reconcile retry budgets, confirm no equivalent attempt is active, then rerun failed jobs.

Azure task logs have limited retention.

Start with the Provision system dependencies task in the linked Azure build logs and compare the first failed steps across AcesShared 61, 73, and 103. Determine the CI provisioning change needed for the iOS 16.0 runtime download failure, then verify terminal reruns no longer fail before repository tests begin.

Written by the indexing model from the issue text.