Bug fix for Update-PSResource not updating from correct repository

[alerickson]

PR Summary

This PR fixes a bug with Update-PSResource where it was not installing from the repository which the previous installation for the lower version had been installed from. Update now looks at the Repository property after retrieving installed version and installs from that repository. The -Repository parameter still takes precedence, so if a user passes in a value there, that will be the repository update uses.

PR Context

Resolves #1521

PR Checklist

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