gsk: Trust return value nullability again

Author: sdroege

gsk4/Gir.toml

@@ -172,7 +172,6 @@ status = "generate"
 [[object]]
 name = "Gsk.Transform"
 status = "generate"
-trust_return_value_nullability = false
     [[object.function]]
     name = "equal"
         [[object.function.parameter]]