[clang-format] Set requires expression params as not an expression

Previously, the parens of a requires expression's "parameters" were not
explicitly set, meaning they ended up as whatever the outer scope was.
This is a problem in some cases though, since the process of determining
star/amp checks if the token is inside of an expression context

This patch always makes sure the context between those parens are always
set to not be an expression

Fixes https://github.com/llvm/llvm-project/issues/59600

Reviewed By: HazardyKnusperkeks, owenpan

Differential Revision: https://reviews.llvm.org/D140330