Changing docstring with demo-code to r-string.

The bytes inside the example weren't properly escaped using a raw string helps. Some IDE's threw an error, readthedocs showed this as empty.

Author: MrSmoer

bleak/__init__.py

@@ -726,7 +726,7 @@ async def write_gatt_char(
         data: Buffer,
         response: bool = None,
     ) -> None:
-        """
+        r"""
         Perform a write operation on the specified GATT characteristic.
 
         There are two possible kinds of writes. *Write with response* (sometimes