Update command: Bad behavior if existing manifest has multiple installer URLs and a URL is provided on cmd-line

[palenshus]

Brief description of your issue

For the Update command, if the existing manifest in winget-pkgs has multiple installer urls, we'll get bad behavior if the URL doesn't specify a URL on the command line.

Steps to reproduce

update -i Microsoft.PowerShell -u https://github.com/PowerShell/PowerShell/releases/download/v7.1.3/PowerShell-7.1.3-win-x64.msi

Expected behavior

Error message indicating that multiple URLs are not supported.

Actual behavior

Update "succeeds" and produces an installer manifest with two nodes with the same URL, but different archs and hashes