Add comment to enum iteration test

Author: ngaya-ll

test-data/unit/pythoneval.test

@@ -1460,6 +1460,10 @@ _testNoCrashOnGenericUnionUnpacking.py:15: error: Revealed type is 'Union[builti
 _testNoCrashOnGenericUnionUnpacking.py:16: error: Revealed type is 'Union[builtins.int*, builtins.str*]'
 
 [case testEnumIteration]
+# Regression test for #2305
+# Tests that:
+# - Mypy allows iteration over enum classes in comprehensions and for-loops
+# - The inferred element type in such iteration contexts is the enum type
 from enum import Enum
 class E(Enum):
     A = 'a'