winget: fix asset/release regexes to match correctly

[ldennington]

We had a couple issues in our release-winget pipeline that were obfuscated by the error we were getting from wingetcreate (fixed with #206) and some confusion with PowerShell variables:

1. We were matching on .exe, meaning we matched on both the Git and PortableGit assets. This caused wingetcreate to attempt to update the Microsoft.Git manifest with both assets and return the initial error that tipped us off to something being amiss: Updating a manifest is only supported with the same number of installer URLs. This has been fixed by instead matching on 64-bit.exe.

2. We were trying to match on the $assets variable, which does not exist in this version of the script. This caused the initial value of $Matches[0] to be saved to the $version variable, and the version that the Microsoft.Git manifest was updated to was 64-bit.exe, rather than 2.34.1.0.0. This was corrected by updating $assets to $github.release.

Here is a repro of the initial failure described in item 1 above:
https://github.com/ldennington/git/runs/4512447452?check_suite_focus=true

Here is a repro of the version error described in item 2 above:
https://github.com/ldennington/git/runs/4513024477?check_suite_focus=true

Here is a successful run with the fixes in place:
https://github.com/ldennington/git/runs/4513446852?check_suite_focus=true

[dscho]

And the Scalar tests finally passed ;-)