[mlir][unittest] Fix crash when building with MSVC 2022

The test Dialect/Affine/ops.mlir was failing when building with
Visual Studio 2022 version 17.3.5. This was caused by a bad MSVC codegen, when
capturing a `constexpr` in a lambda. The bug was reported to Microsoft, see
differential for more information.

Differential revision: https://reviews.llvm.org/D134227