### 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)

return true;
			} else if (components[1] == "coords_level") {
				for (int i = 0; i < a.size(); i += 2) {
					Array key = a[i];
					Array value = a[i + 1];
					set_coords_level_tile_proxy(key[0], key[1], value[0], value[1]);
				}
				return true;
			} else if (components[1] == "alternative_level") {
				for (int i = 0; i < a.size(); i += 2) {
					Array key = a[i];
					Array value = a[i + 1];
					set_alternative_level_tile_proxy(key[0], key[1], key[2], value[0], value[1], value[2]);
				}
				return true;
			}
			return false;
		} else if (components.size() == 1 && components[0].begins_with("pattern_") && components[0].trim_prefix("pattern_").is_valid_int()) {
			int pattern_index = components[0].trim_prefix("pattern_").to_int();
			for (int i = patterns.size(); i <= pattern_index; i++) {
				add_pattern(p_value);
			}
			return true;
		}
#ifndef DISABLE_DEPRECATED
	}
#endif 
	return false;
}
bool TileSet::_get(const StringName &p_name, Variant &r_ret) const {