python
DOC: add missing `versionadded` metadata for `TypeAlias`
According to git blame, TypeAlias was added in https://github.com/python/typing_extensions/commit/d362ccb6504bf52618796822e8e6ffa9091575a4, which GitHub's UI indicates was included as early as 3.10.0.0
We didn't track version changes before 4.0 very well. There are many other objects added before 4.0 that also don't have a versionadded note, so I'd rather not add it for just one of them.
4.0 is almost four years old at this point so I don't see much point in tracking down exactly when in the 3.* series each object was added.
I see. The reason I opened this is that I only needed this single feature and wanted to define my dependency on typing-extension in the loosest (yet correct) way, so I went to search this specific bit of information and added it back when I got it. I understand if only doing this (very) partially isn't desired. However, I would suggest adding a note somewhere saying that whenever this information is missing, 4.0.0 is a safe minimum requirement to assume, because this isn't obvious at all from the outside.