Need add test for that libspdm properly calls and handles the verify cert callback functions

[Wenxing-hou]

Refer to the PR: #2672 feedback,

Testing that libspdm properly calls and handles the output of Integrator-provided functions.
For example there is currently no coverage for verify_peer_spdm_cert_chain in [GET_CERTIFICATE] and encapsulated [GET_CERTIFICATE].
This would be tested in the unit tests for the corresponding SPDM message. For example test_spdm_requester/get_certificate.c.
Note that the callback function used for testing need not be elaborate. It can just return true or false.

Need add the unit_test for that libspdm properly calls and handles the verify cert callback functions.