DangerousFileDetectorTests.ItShouldDetectFileWithMarkOfTheWeb fails on IE-less vs2026.pre.scout image

### Summary

`Microsoft.DotNet.Cli.Utils.Tests.DangerousFileDetectorTests.ItShouldDetectFileWithMarkOfTheWeb` fails on the new **`windows.amd64.vs2026.pre.scout`** CI image (Windows Server 2025 + VS 2026 preview, with Internet Explorer removed).

```
Expected boolean to be True, but found False.
```

### Root cause

The test writes a `Zone.Identifier` alternate data stream (`ZoneId=3`, Internet zone) and asserts that `DangerousFileDetector.IsDangerous(file)` returns `true`. `DangerousFileDetector` relies on the legacy IE/urlmon `InternetSecurityManager` and `MapUrlToZone`.

On the IE-stripped scout image this is **unreliable and inconsistent**:

- The `InternetSecurityManager` COM class still instantiates (urlmon is present), but `MapUrlToZone` no longer reliably honors the `Zone.Identifier` stream.
- Worse, the behavior **diverges between code paths**: an independent `MapUrlToZone` probe can report the file as Internet zone (`zone >= URLZONE_INTERNET`) while the product's `DangerousFileDetector.IsDangerous` (CsWin32 path) reports it as *not* dangerous on the same image. So capability-gating the assertion on an independent probe does not work — the gate and the product disagree.

### Repro

- Build [1477806](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1477806) (PR #54945), `TestBuild: windows (x64)` leg on `windows.amd64.vs2026.pre.scout.open`.

### Mitigation

Disabling the test on the affected image via `[Ignore]` pointing at this issue.

### Follow-up

Decide on a robust long-term approach, e.g.:
- Assert only the deterministic negative case (a file without Mark-of-the-Web is never dangerous), and drop the environment-dependent positive assertion; or
- Reliably detect functional Mark-of-the-Web support before asserting; or
- Skip the positive assertion on images where the IE/urlmon zone manager is non-functional.

Start with Microsoft.DotNet.Cli.Utils.Tests.DangerousFileDetectorTests.ItShouldDetectFileWithMarkOfTheWeb and the DangerousFileDetector.IsDangerous path, then reproduce the failure on the windows.amd64.vs2026.pre.scout image using build 1477806. Compare the test's Zone.Identifier setup with the CsWin32 and InternetSecurityManager behavior; done means the test has a deterministic, reliable outcome on supported and IE-less images.

Written by the indexing model from the issue text.