Update command shouldn't submit PR if there's no changes

[palenshus]

Brief description of your issue

When wingetcreate update is run with just a packageId, it'll fetch the package at the current URL, hash it, and submit an update PR. This makes sense if the URL is a vanity URL and the version is "latest", but not in other cases. For example, see this PR microsoft/winget-pkgs#17720 (comment)

Steps to reproduce

wingetcreate update GitHub.cli -s

Expected behavior

Aborts after determining that there's no substantial changes to be made

Actual behavior

Downloads package at current URL, hashes it (resulting in the same hash), and submits a PR with no real changes