Fix wrong regex for WP 10+

[kkmuffme]

In this PR:

• Version_Utils - Adds support for "XX.X" WordPress version format. Earlier "X.X" was only supported.
• Added unit tests for the change

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Co-authored-by: ernilambar <rabmalin@git.wordpress.org>
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[ernilambar]

Thanks for the PR. Can you please add some tests for the change? Thanks.

[kkmuffme]

If there were any tests that tested the previous behavior I could, but I don't have the time to create completely new ones. Since you co-authored, I guess that's the part where you come in? :-)