Updated the TC_CNET_4_15.py by adding chip.testing.matter_testing (#39238)

Author: KishokG

src/python_testing/TC_CNET_4_15.py

@@ -20,8 +20,7 @@
 import logging
 
 import chip.clusters as Clusters
-from matter_testing_infrastructure.chip.testing.matter_testing import (MatterBaseTest, TestStep, default_matter_test_main,
-                                                                       has_feature, run_if_endpoint_matches)
+from chip.testing.matter_testing import MatterBaseTest, TestStep, default_matter_test_main, has_feature, run_if_endpoint_matches
 from mobly import asserts