### 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)

while (scenes.has(next_scene_id)) {
		next_scene_id = (next_scene_id % 1073741823) + 1; 
	};
}
int TileSetScenesCollectionSource::get_tiles_count() const {
	return 1;
}
Vector2i TileSetScenesCollectionSource::get_tile_id(int p_tile_index) const {
	ERR_FAIL_COND_V(p_tile_index != 0, TileSetSource::INVALID_ATLAS_COORDS);
	return Vector2i();
}
bool TileSetScenesCollectionSource::has_tile(Vector2i p_atlas_coords) const {
	return p_atlas_coords == Vector2i();
}
int TileSetScenesCollectionSource::get_alternative_tiles_count(const Vector2i p_atlas_coords) const {
	return scenes_ids.size();
}
int TileSetScenesCollectionSource::get_alternative_tile_id(const Vector2i p_atlas_coords, int p_index) const {
	ERR_FAIL_COND_V(p_atlas_coords != Vector2i(), TileSetSource::INVALID_TILE_ALTERNATIVE);
	ERR_FAIL_INDEX_V(p_index, scenes_ids.size(), TileSetSource::INVALID_TILE_ALTERNATIVE);
	return scenes_ids[p_index];
}
bool TileSetScenesCollectionSource::has_alternative_tile(const Vector2i p_atlas_coords, int p_alternative_tile) const {