[stdlib] Add more default values (#14632)

stdlib/_csv.pyi

@@ -36,7 +36,7 @@ class Dialect:
     strict: bool
     def __new__(
         cls,
-        dialect: _DialectLike | None = ...,
+        dialect: _DialectLike | None = None,
         delimiter: str = ",",
         doublequote: bool = True,
         escapechar: str | None = None,