Fix typo in test_dataclasses.py (gh-95735)

`dataclass` was called as a function when it was almost certainly intended to be a decorator.
(cherry picked from commit 59e09ef)

Co-authored-by: da-woods <[email protected]>

Author: miss-islington

Lib/test/test_dataclasses.py

@@ -2129,12 +2129,12 @@ class C(B):
         self.assertEqual(c.z, 100)
 
     def test_no_init(self):
-        dataclass(init=False)
+        @dataclass(init=False)
         class C:
             i: int = 0
         self.assertEqual(C().i, 0)
 
-        dataclass(init=False)
+        @dataclass(init=False)
         class C:
             i: int = 2
             def __init__(self):