Fixed error with mypy [skip ci]

Author: ankane

pgvector/django/extensions.py

@@ -3,9 +3,8 @@
 
 
 class VectorExtension(CreateExtension):
-    if VERSION[0] >= 6:
-        def __init__(self, hints=None):
+    def __init__(self, hints=None):
+        if VERSION[0] >= 6:
             super().__init__('vector', hints=hints)
-    else:
-        def __init__(self):
+        else:
             self.name = 'vector'