[clang] [Clang] Fix the instantiation of return type requirements in lambda bodies (PR #76967)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This is a not-awful way of solving this until we stop instantiating the body of the lambda.  Could you please comment to that effect in TransformLambdaBody?

Also would like @cor3ntin to take a look as well, else i'm ok with this.

https://github.com/llvm/llvm-project/pull/76967