[clang] [clang] Fix eager skipping on new with unknown type and no new-initializer (PR #110133)

[via cfe-commits]

https://github.com/Sirraide approved this pull request.

LGTM.

`ParseExpressionList()` is used in a lot of places, but given that almost all the other tests seem to have no problem with this change (which honestly surprises me a bit), I feel like this is reasonable (in the tests that are affected, we gain a bogus diagnostic in one and lose one in another, so imo that evens out ;Þ), and a more accurate AST in is always nice.

https://github.com/llvm/llvm-project/pull/110133