[flang][NFC] Add tests for fir.array_modify in array-value-copy pass

This patch adds some test for the `fir.array_modify` operation
in the array-value-copy pass

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D122809



Co-authored-by: V Donaldson <vdonaldson@nvidia.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>