Update ctk_progressbar.py

[DenishKakadiya]

#2606

• replaced 50 with 100 to properly calculate determinate_value from determinate_speed value.

This change will correct wierd output of determinate_value for each step increament.

[FedericoSpada]

Hi,
I think that the division by 50 is because _internal_loop() is called every 20ms, so that determinate_speed and indeterminate_speed can be considered to have [%/s] as unit of measurement.

In case we call step() manually, that unit of measurement is no longer applicable. For this reason, I would suggest creating a new separated parameter (called, for example, "step_increment") that will be used just when the step() method is invoked. Its unit of measurement would be [%], and it would be used as is without any other division.