[mlir] Always create a list of alias scopes when emitting LLVM IR

Previously, the translation to LLVM IR would emit IR that directly uses
a scope metadata node in case only one scope was in use in alias.scopes
or noalias metadata. It should always be a list of scopes. The verifier
change in 8700f2bd enforced this and
broke the test. Fix the translation to always create a list of scopes
using a new metadata node, update and reenable the respective test.

Fixes PR51919.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D110140