Google has updated the localized versions of your page help document to change all the hreflang examples from lowercase codes to uppercase codes. It doesn't matter because the hreflang value is case-insensitive; Google accepts lowercase and uppercase codes.
Google also posted a new line that explains why the change to uppercase, Google wrote:
The hreflang value is case-insensitive; Google accepts lowercase and uppercase codes, but formatting region codes in uppercase (for example, en-GB) follows ISO 3166-1 Alpha 2 convention.
Here is a screenshot of the text added to this help document:
Here is what the old page had, as an example:
Here is the new version with uppercase codes:
You should probably be consistent when you do the uppercase or lowercase codes but hey, Google did change all their documentation to uppercase.
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