### 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 (KeyValue<Vector2i, TileAlternativesData> E_tile : tiles) {
		for (KeyValue<int, TileData *> E_alternative : E_tile.value.alternatives) {
			E_alternative.value->remove_physics_layer(p_index);
		}
	}
}
void TileSetAtlasSource::add_terrain_set(int p_to_pos) {
	for (KeyValue<Vector2i, TileAlternativesData> E_tile : tiles) {
		for (KeyValue<int, TileData *> E_alternative : E_tile.value.alternatives) {
			E_alternative.value->add_terrain_set(p_to_pos);
		}
	}
}
void TileSetAtlasSource::move_terrain_set(int p_from_index, int p_to_pos) {
	for (KeyValue<Vector2i, TileAlternativesData> E_tile : tiles) {
		for (KeyValue<int, TileData *> E_alternative : E_tile.value.alternatives) {
			E_alternative.value->move_terrain_set(p_from_index, p_to_pos);
		}
	}
}
void TileSetAtlasSource::remove_terrain_set(int p_index) {
	for (KeyValue<Vector2i, TileAlternativesData> E_tile : tiles) {
		for (KeyValue<int, TileData *> E_alternative : E_tile.value.alternatives) {
			E_alternative.value->remove_terrain_set(p_index);
		}
	}
}
void TileSetAtlasSource::add_terrain(int p_terrain_set, int p_to_pos) {