[Keras 3 OpenVINO Backend]: Improve test code `CoreOpsCallsTests`

[daehyun99]

Request Description

This issue tracks improving test code CoreOpsCallsTests in the Keras OpenVINO backend.

It appears that the CoreOpsCallsTests class listed in excluded_concrete_tests.txt has not been implemented yet.

keras/keras/src/backend/openvino/excluded_concrete_tests.txt

Lines 49 to 52 in dc3bdb1

	CoreOpsCallsTests::test_fori_loop_basic_functionality
	CoreOpsCallsTests::test_map_basic_call
	CoreOpsCallsTests::test_switch_basic_call
	CoreOpsCallsTests::test_unstack_basic_functionality

I will submit a PR implementing this and enable the corresponding tests.

Thanks.