[New Feature]: Manifest version 1.6.0 should have been flagged from the pipeline

### Description of the new feature/enhancement

Follow up from https://github.com/microsoft/winget-pkgs/pull/373842#issuecomment-4549587738 and how common new commers uses `ManifestVersion: 1.6.0` instead of latest, I think any PR submitted with said `ManifestVersion` should have been flagged as https://github.com/microsoft/winget-pkgs/labels/Manifest-Version-Deprecated to match with the docs deprecation label:

Just like what's already did for even older schema versions (e.g.: https://github.com/microsoft/winget-pkgs/pull/378423#issuecomment-4529529552).

### Proposed technical implementation details (optional)

_No response_

Start by reviewing the manifest validation pipeline and the linked pull request examples, especially the existing handling for older schema versions. Trace where ManifestVersion values are checked and labels are applied. Done means submissions using ManifestVersion 1.6.0 receive the Manifest-Version-Deprecated label consistently with older deprecated versions.

Written by the indexing model from the issue text.