Resolved An object rotated by a script increases its speed at the beginning and end of the rotation

There is a simple code that rotates an object in a semicircle with radius 1 around the point 0,0,0.
How I do it: I smoothly change the "X" coordinate from -1 to 1 and calculate the "Y" coordinate using the Pythagorean theorem:

For some reason it speeds up at the beggining and at the end of the animation:

How to make the rotation speed constant?

 

this code works!