synthio: one more doc fix

Author: jepler

shared-bindings/synthio/__init__.c

@@ -67,7 +67,7 @@ static const mp_arg_t envelope_properties[] = {
 //| BlockInput = Union["Math", "LFO", float, None]
 //| """Blocks and Notes can take any of these types as inputs on certain attributes
 //|
-//| A BlockInput can be any of the following types: `Math`, `LFO`, `float`, `None` (treated same as 0).
+//| A BlockInput can be any of the following types: `Math`, `LFO`, `builtins.float`, `None` (treated same as 0).
 //| """
 //|
 //| class Envelope: