### 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_list->push_back(PropertyInfo(Variant::NIL, GNAME("Custom Data", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
	for (int i = 0; i < custom_data_layers.size(); i++) {
		p_list->push_back(PropertyInfo(Variant::STRING, vformat("custom_data_layer_%d/name", i)));
		p_list->push_back(PropertyInfo(Variant::INT, vformat("custom_data_layer_%d/type", i), PROPERTY_HINT_ENUM, argt));
	}
	
	
	for (const KeyValue<int, Ref<TileSetSource>> &E_source : sources) {
		p_list->push_back(PropertyInfo(Variant::INT, vformat("sources/%d", E_source.key), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR));
	}
	
	
	p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Tile Proxies", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
	p_list->push_back(PropertyInfo(Variant::ARRAY, PNAME("tile_proxies/source_level"), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR));
	p_list->push_back(PropertyInfo(Variant::ARRAY, PNAME("tile_proxies/coords_level"), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR));
	p_list->push_back(PropertyInfo(Variant::ARRAY, PNAME("tile_proxies/alternative_level"), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR));
	
	for (unsigned int pattern_index = 0; pattern_index < patterns.size(); pattern_index++) {
		p_list->push_back(PropertyInfo(Variant::OBJECT, vformat("pattern_%d", pattern_index), PROPERTY_HINT_RESOURCE_TYPE, "TileMapPattern", PROPERTY_USAGE_NO_EDITOR));
	}
}
void TileSet::_validate_property(PropertyInfo &p_property) const {
	if (p_property.name == "tile_layout" && tile_shape == TILE_SHAPE_SQUARE) {
		p_property.usage ^= PROPERTY_USAGE_READ_ONLY;
	} else if (p_property.name == "tile_offset_axis" && tile_shape == TILE_SHAPE_SQUARE) {
		p_property.usage ^= PROPERTY_USAGE_READ_ONLY;
	}
}
void TileSet::_bind_methods() {