Fix Aspire Dashboard product version resolution in update-dependencies

[lbussell]

Related: #6830

The product version calculation for Aspire Dashboard introduced in #6726 was slightly incorrect. This PR fixes it.

Before this change:

    "aspire-dashboard|build-version": "13.1.0-preview.1.25568.1",
    "aspire-dashboard|product-version": "13.1.0-preview.1.25568.1",
    "aspire-dashboard|fixed-tag": "13.1.0-preview.1.25568.1",
    "aspire-dashboard|minor-tag": "13.1",

After this change:

    "aspire-dashboard|build-version": "13.1.0-preview.1.25568.1",
    "aspire-dashboard|product-version": "13.1.0",
    "aspire-dashboard|fixed-tag": "13.1.0",
    "aspire-dashboard|minor-tag": "13.1",