Replace panther_analysis_tool import with updated import (#1230)

global_helpers/global_helpers_test.py

@@ -10,7 +10,7 @@
 import sys
 import unittest
 
-from panther_analysis_tool.immutable import ImmutableCaseInsensitiveDict, ImmutableList
+from panther_core.immutable import ImmutableCaseInsensitiveDict, ImmutableList
 
 # pipenv run does the right thing, but IDE based debuggers may fail to import
 #   so noting, we append this directory to sys.path