### 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)

}
					p.pop_front();
				}
			}
		} else if (what == "shapes") {
			Array p = p_value;
			for (int i = 0; i < p.size(); i++) {
				CompatibilityShapeData csd;
				Dictionary d = p[i];
				for (int j = 0; j < d.size(); j++) {
					String key = d.get_key_at_index(j);
					if (key == "autotile_coord") {
						csd.autotile_coords = d[key];
					} else if (key == "one_way") {
						csd.one_way = d[key];
					} else if (key == "one_way_margin") {
						csd.one_way_margin = d[key];
					} else if (key == "shape") {
						csd.shape = d[key];
					} else if (key == "shape_transform") {
						csd.transform = d[key];
					}
				}
				ctd->shapes.push_back(csd);
			}
		} else if (what == "occluder") {
			ctd->occluder = p_value;
		} else if (what == "navigation") {
			ctd->navigation = p_value;
			/*