Handle assert_never() when imported from typing_extensions

doc/whatsnew/fragments/9780.false_positive

@@ -0,0 +1,3 @@
+Treat `assert_never()` the same way when imported from `typing_extensions`.
+
+Closes #9780

pylint/checkers/variables.py

@@ -32,7 +32,7 @@
     is_sys_guard,
     overridden_method,
 )
-from pylint.constants import PY311_PLUS, TYPING_NEVER, TYPING_NORETURN
+from pylint.constants import TYPING_NEVER, TYPING_NORETURN
 from pylint.interfaces import CONTROL_FLOW, HIGH, INFERENCE, INFERENCE_FAILURE
 from pylint.typing import MessageDefinitionTuple
 
@@ -944,8 +944,7 @@ def _defines_name_raises_or_returns(name: str, node: nodes.NodeNG) -> bool:
             if utils.is_terminating_func(node.value):
                 return True
             if (
-                PY311_PLUS
-                and isinstance(node.value.func, nodes.Name)
+                isinstance(node.value.func, nodes.Name)
                 and node.value.func.name == "assert_never"
             ):
                 return True

tests/functional/u/used/used_before_assignment_py311.py

@@ -1,6 +1,12 @@
 """assert_never() introduced in 3.11"""
 from enum import Enum
-from typing import assert_never
+
+from pylint.constants import PY311_PLUS
+
+if PY311_PLUS:
+    from typing import assert_never  # pylint: disable=no-name-in-module
+else:
+    from typing_extensions import assert_never
 
 
 class MyEnum(Enum):