First 3d game animation fixes

[docrinehart]

This PR aims to replace screenshots and add a minor warning regarding the node target for keyframes in the Godot First 3D Game tutorial. -- Relates to comment on issue: #6744

While the guide correctly states to get animation keyframes from the Character node, all the subsequent screenshots that show the animation panel have Player showing as the target node. This threw me off for a good 40 minutes until I came across a reddit answer highlighting that the root Player shouldn't be used for keyframes. The issue this causes is that the player character is animated and floating, but no longer moves to player input.

I put in the warning the best explanation I could as far as I understood the issue I had. I'd love to see a more specific or precise explanation added for those learning new concepts.

[AThousandShips]

Please convert the image to the .webp format.
you can read more about it in the Doc image guidelines.

[skyace65]

Thanks! And congrats on your first merged PR!

[docrinehart]

Thanks! And congrats on your first merged PR!

Thank you! Glad I was able to contribute. Hopefully I'll find some time to get in the weeds for the engine itself and make some contributions there.

[mhilbrunner]

Cherry-picked to 4.2 in #9648.