Add regression test from #2306 (#4570)

Author: nelfin

tests/functional/r/regression/regression_2306_enum_value.py

@@ -0,0 +1,11 @@
+# pylint: disable=missing-docstring,invalid-name
+
+from enum import Enum
+
+class Color(Enum):
+    red = 1
+    green = 2
+    blue = 3
+
+    def __lt__(self, other):
+        return self.value < other.value