### Godot version

5ee983188de97ae027f9b9c1443438063f708a7e

### System information

Windows 11

### Issue description

Godot editor will throw an error and fail to generate preview icons for terrain tiles which use a base image which is not RGBA8 format.
`core\io\image.cpp:2788 - Condition "format != p_src->format" is true.`

### Steps to reproduce

- Import a non-RGBA8 image into Godot.
- Create a TileMap
- Create an associated TileSet
- Create a terrain for this tileset
- Add the image as an atlas
- Go to the paint tab
- Paint the terrain on the TileSet
- An error will occur any time terrains are edited in the TileSet editor or selected in the TileMap editor terrain tab.

### Minimal reproduction project

[tileset_terrain_bug.zip](https://github.com/godotengine/godot/files/13264213/tileset_terrain_bug.zip)

if (components[1] == "size_in_atlas") {
				move_tile_in_atlas(coords, coords, p_value);
				return true;
			} else if (components[1] == "next_alternative_id") {
				tiles[coords].next_alternative_id = p_value;
				return true;
			} else if (components[1] == "animation_columns") {
				set_tile_animation_columns(coords, p_value);
				return true;
			} else if (components[1] == "animation_separation") {
				set_tile_animation_separation(coords, p_value);
				return true;
			} else if (components[1] == "animation_speed") {
				set_tile_animation_speed(coords, p_value);
				return true;
			} else if (components[1] == "animation_mode") {
				set_tile_animation_mode(coords, VariantCaster<TileSetAtlasSource::TileAnimationMode>::cast(p_value));
				return true;
			} else if (components[1] == "animation_frames_count") {
				set_tile_animation_frames_count(coords, p_value);
				return true;
			} else if (components.size() >= 3 && components[1].begins_with("animation_frame_") && components[1].trim_prefix("animation_frame_").is_valid_int()) {
				int frame = components[1].trim_prefix("animation_frame_").to_int();
				if (components[2] == "duration") {
					if (frame >= get_tile_animation_frames_count(coords)) {
						set_tile_animation_frames_count(coords, frame + 1);
					}
					set_tile_animation_frame_duration(coords, frame, p_value);
					return true;