[Clang][Parser] Have the depth of the abbreviated generic lambdas inside a...

[Clang][Parser] Have the depth of the abbreviated generic lambdas inside a requires clause differ from the surrounding generic lambda (#80656)

A one-line fix, again : )

This fixes https://github.com/llvm/llvm-project/issues/78524 and the
similar example at
https://github.com/llvm/llvm-project/issues/78524#issuecomment-1899886951.

We previously increased the template depth by one after parsing the
attaching requires-clause on a lambda expression. This led to a problem
where the 'auto' parameters of nested abbreviated generic lambdas,
inside of a requires-expression, had the same depth as the template
parameters of the surrounding lambda. Consequently, during the
concept-checking stage, we ended up substituting these parameters with
the wrong template arguments because they were at different levels.