[Attributor][FIX] Visit same instructions with different scopes

If we collect potential values we need to visit a value even if we have
seen it before if the scope is different. The scope is part of the
result after all. Test included.

Fixes https://github.com/llvm/llvm-project/issues/56753

Differential Revision: https://reviews.llvm.org/D131597

(cherry picked from commit b65471d7)