Use 3.9 syntax + count dunder calls

Author: svalentin

mypyc/test-data/irbuild-classes.test

@@ -1381,4 +1381,3 @@ class M(type):  # E: Inheriting from most builtin types is unimplemented
 @mypyc_attr(native_class=True)
 class A(metaclass=M):  # E: Class is marked as native_class=True but it can't be a native class
     pass
-

mypyc/test-data/run-classes.test

@@ -2890,20 +2890,28 @@ def test_function():
 
 [case testMypycAttrNativeClassDunder]
 from mypy_extensions import mypyc_attr
-from typing import Generic, TypeVar
+from typing import Generic, Optional, TypeVar
 
 _T = TypeVar("_T")
 
+get_count = set_count = del_count = 0
+
 @mypyc_attr(native_class=False)
 class Bar(Generic[_T]):
     # Note the lack of __deletable__
     def __init__(self) -> None:
         self.value: str = 'start'
-    def __get__(self, instance: _T, owner: type[_T] | None = None) -> str:
+    def __get__(self, instance: _T, owner: Optional[type[_T]] = None) -> str:
+        global get_count
+        get_count += 1
         return self.value
     def __set__(self, instance: _T, value: str) -> None:
+        global set_count
+        set_count += 1
         self.value = value
     def __delete__(self, instance: _T) -> None:
+        global del_count
+        del_count += 1
         del self.value
 
 @mypyc_attr(native_class=False)
@@ -2915,11 +2923,15 @@ import native
 
 f = native.Foo()
 assert(hasattr(f, 'bar'))
+assert(native.get_count == 1)
 assert(f.bar == 'start')
+assert(native.get_count == 2)
 f.bar = 'test'
 assert(f.bar == 'test')
+assert(native.set_count == 1)
 del f.bar
 assert(not hasattr(f, 'bar'))
+assert(native.del_count == 1)
 
 [case testMypycAttrNativeClassMeta]
 from mypy_extensions import mypyc_attr