Fix LED Tester AssertDutyCycle

[fipsi7]

Fixes renode/renode#786

The current check for the LED Duty Cycle isn't correct.

Because of the check at the beginning:
in src/Emulator/Main/Testing/LEDTester.cs

ValidateArgument(expectedDutyCycle, nameof(expectedDutyCycle), min: 0, max: 1);
ValidateArgument(tolerance, nameof(tolerance), min: 0, max: 1);

This

if(highPercentage < expectedDutyCycle - (tolerance * 100) || expectedDutyCycle > expectedDutyCycle + (tolerance * 100))

should be this:

if(highPercentage < ((expectedDutyCycle - tolerance) * 100) || highPercentage > ((expectedDutyCycle + tolerance) * 100))