Add a regression test for AttributeError for Subscript object

Closes #4439

ChangeLog

@@ -17,6 +17,11 @@ Release date: TBA
 ..
   Put bug fixes that should not wait for a new minor version here
 
+* Fix a crash when there would be a 'TypeError object does not support
+  item assignment' in the code we parse.
+
+  Closes #4439
+
 * Fix crash if a callable returning a context manager was assigned to a list or dict item
 
   Closes #4732

tests/functional/r/regression/regression_4439.py

@@ -0,0 +1,13 @@
+"""AttributeError: 'Subscript' object has no attribute 'name' """
+# pylint: disable=missing-docstring
+
+from typing import Optional
+
+from attr import attrib, attrs
+
+
+@attrs()
+class User:
+    name: str = attrib()
+    age: int = attrib()
+    occupation = Optional[str] = attrib(default=None) # [unsupported-assignment-operation]

tests/functional/r/regression/regression_4439.txt

@@ -0,0 +1 @@
+unsupported-assignment-operation:13:17:User:'Optional' does not support item assignment:HIGH