### 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 {
			return false;
		}
	} else if (components.size() == 2 && components[0] == "tile_proxies") {
		if (components[1] == "source_level") {
			Array a;
			for (const KeyValue<int, int> &E : source_level_proxies) {
				a.push_back(E.key);
				a.push_back(E.value);
			}
			r_ret = a;
			return true;
		} else if (components[1] == "coords_level") {
			Array a;
			for (const KeyValue<Array, Array> &E : coords_level_proxies) {
				a.push_back(E.key);
				a.push_back(E.value);
			}
			r_ret = a;
			return true;
		} else if (components[1] == "alternative_level") {
			Array a;
			for (const KeyValue<Array, Array> &E : alternative_level_proxies) {
				a.push_back(E.key);
				a.push_back(E.value);
			}
			r_ret = a;
			return true;
		}