Update librt.strings stub

Author: JukkaL

mypy/typeshed/stubs/librt/librt/strings.pyi

@@ -4,7 +4,7 @@ from mypy_extensions import i64, i32, u8
 
 @final
 class BytesWriter:
-    def append(self, /, x: int) -> None: ...
+    def append(self, x: int, /) -> None: ...
     def write(self, b: bytes | bytearray, /) -> None: ...
     def getvalue(self) -> bytes: ...
     def truncate(self, size: i64, /) -> None: ...