Fix animation name in Your first 2D game

[Calinou]

• See getting_started/first_2d_game/02.player_scene godot-docs-user-notes#105 (comment).

[mhilbrunner]

Thank you, merged.

[Piralein]

This change is wrong in my opinion.
The images are called playerGrey_up1.png, playerGrey_up2.png and playerGrey_walk1.png, playerGrey_walk2.png.

playerGrey_up[1/2] means playerGrey_up1.png and playerGrey_up2.png
playerGrey_walk[1/2] means playerGrey_walk1.png and playerGrey_walk2.png

Drag the two images for each animation, named...

[Dreyseth]

The file names are not the problem here. The issue is in readability of the text "[1/2]", which reads as "one OF two" rather than the intended "one AND two".

[mhilbrunner]

Cherry-picked to 4.3 in #10038.