### 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)

}
					}
				}
			}
		}
	}
	
	for (int terrain_set = 0; terrain_set < get_terrain_sets_count(); terrain_set++) {
		for (int terrain = 0; terrain < get_terrains_count(terrain_set); terrain++) {
			Ref<Image> image;
			image.instantiate();
			if (counts[terrain_set][terrain].count > 0) {
				
				Ref<Texture2D> texture = counts[terrain_set][terrain].texture;
				Rect2i region = counts[terrain_set][terrain].region;
				image->initialize_data(region.size.x, region.size.y, false, Image::FORMAT_RGBA8);
				image->blit_rect(texture->get_image(), region, Point2i());
				image->resize(p_size.x, p_size.y, Image::INTERPOLATE_NEAREST);
			} else {
				image->initialize_data(1, 1, false, Image::FORMAT_RGBA8);
				image->set_pixel(0, 0, get_terrain_color(terrain_set, terrain));
			}
			Ref<ImageTexture> icon = ImageTexture::create_from_image(image);
			icon->set_size_override(p_size);
			output.write[terrain_set].write[terrain] = icon;
		}
	}
	return output;
}
void TileSet::_source_changed() {