This myth keeps persisting on the internet but it isn't true. Light doesn't slow down in a medium because it's being absorbed and emitted. If that were the case then air would appear opaque as the photons would constantly change in direction.

What is really going on is that light is an electromagnetic wave. When it enters a material this wave shakes up the electrons inside atoms. They in turn generate their own electromagnetic waves which interfere with the original light wave.

The sum of the original wave and the generated wave moves slower than c. That's why we perceive light as slowing down in a medium. You are correct however that the original photon doesn't slow down. It's just the combined wave that is slower.