[Clang] Fix the trailing comma regression (#136273)
925e195 introduced a regression since which we started to accept invalid
trailing commas in many expression lists where they're not allowed by
the grammar. The issue came from the fact that an additional invalid
state - previously handled by ParseExpressionList - was overlooked in
that patch.
Fixes https://github.com/llvm/llvm-project/issues/136254
No release entry because I want to backport it.
