csv: csv.reader and csv.writer - mark csvfile as positional only

Author: adamtheturtle

stdlib/_csv.pyi

@@ -90,6 +90,7 @@ else:
 
 def writer(
     csvfile: SupportsWrite[str],
+    /,
     dialect: _DialectLike = "excel",
     *,
     delimiter: str = ",",
@@ -103,6 +104,7 @@ def writer(
 ) -> _writer: ...
 def reader(
     csvfile: Iterable[str],
+    /,
     dialect: _DialectLike = "excel",
     *,
     delimiter: str = ",",