fix: Add cmake missing source file ref for core_lowering.passes

[Arktische]

Description

Add missing source file core/lowering/passes/unpack_scaled_dot_product_attention.cpp to core/lowering/passes/CMakeLists.txt. If not do so, when building shared library torchtrt will fail due to missing reference to function UnpackScaledDotProductAttention.

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project (You can use the linters)
• I have added the relevant labels to my PR in so that relevant reviewers are notified
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes

[narendasan]

LGTM, Thanks!