"Animation Track types" page doesn't specify that some track types won't work backwards

**Your Godot version:** 4.5

**Issue description:** The page describing Animation Track types doesn't point out that Animation Playback tracks will not play when the animation is played with `play_backwards()`. I'd made an animation that used these kinds of tracks, and then was confused because they were not playing correctly (or at all) when I used `play_backwards()` on them.

It'd be good to have this page specify that Animation Tracks, and likely other track types as well, will not work in reverse or with different speed scales.

**URL to the documentation page:** https://docs.godotengine.org/en/stable/tutorials/animation/animation_track_types.html