Fix signature

Author: KitaitiMakoto

bindings/ruby/sig/whisper.rbs

@@ -49,7 +49,7 @@ module Whisper
             | (Params, _Samples, ?Integer n_samples) -> self
     def full_parallel: (Params, Array[Float], ?Integer n_samples) -> self
                      | (Params, _Samples, ?Integer n_samples) -> self
-                     | (Params, _Samples, ?Integer? n_samples, Integer n_processors) -> void
+                     | (Params, _Samples, ?Integer? n_samples, Integer n_processors) -> self
   end
 
   class Params