### 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)

} 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 (frame < 0 || frame >= get_tile_animation_frames_count(coords)) {
						return false;
					}
					if (components[2] == "duration") {
						r_ret = get_tile_animation_frame_duration(coords, frame);
						return true;
					}
					return false;
				} else if (components[1].is_valid_int()) {
					int alternative_id = components[1].to_int();
					if (alternative_id != TileSetSource::INVALID_TILE_ALTERNATIVE && tiles[coords].alternatives.has(alternative_id)) {
						if (components.size() >= 3) {
							bool valid;
							r_ret = tiles[coords].alternatives[alternative_id]->get(components[2], &valid);
							return valid;
						} else {
							
							r_ret = alternative_id;
							return true;
						}
					}
				}
			}
		}
	}
	return false;
}
void TileSetAtlasSource::_get_property_list(List<PropertyInfo> *p_list) const {