[DO NOT MERGE] 3D weakly_conforming -> nonconforming Override Test

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Description

This PR satisfies the following task

• On a temporary branch, modify core/specfem/assembly/element_intersections/dim3/element_intersections.cpp to override acoustic-elastic intersections to the nonconforming connection type

• issue PR on this branch -- the relevant displacement_tests should still pass for all configurations listed on CI.

Changes to this branch in order to satisfy the above task will be PR'ed into devel after success (whether separate PR, or edit to this one).

Issue Number

If there is an issue created for these changes, link it here

Checklist

Please make sure to check developer documentation on specfem docs.

• I ran the code through pre-commit to check style
• THE DOCUMENTATION BUILDS WITHOUT WARNINGS/ERRORS
• I have added labels to the PR (see right hand side of the PR page)
• My code passes all the integration tests
• I have added sufficient unittests to test my changes
• I have added/updated documentation for the changes I am proposing
• I have updated CMakeLists to ensure my code builds
• My code builds across all platforms