### 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)

if (p_name == "tile_data") {
		r_ret = _get_tile_data();
		return true;
	}
	return false;
}
void TileMapPattern::_get_property_list(List<PropertyInfo> *p_list) const {
	p_list->push_back(PropertyInfo(Variant::OBJECT, "tile_data", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NO_EDITOR | PROPERTY_USAGE_INTERNAL));
}
void TileMapPattern::_bind_methods() {
	ClassDB::bind_method(D_METHOD("set_cell", "coords", "source_id", "atlas_coords", "alternative_tile"), &TileMapPattern::set_cell, DEFVAL(TileSet::INVALID_SOURCE), DEFVAL(TileSetSource::INVALID_ATLAS_COORDS), DEFVAL(TileSetSource::INVALID_TILE_ALTERNATIVE));
	ClassDB::bind_method(D_METHOD("has_cell", "coords"), &TileMapPattern::has_cell);
	ClassDB::bind_method(D_METHOD("remove_cell", "coords", "update_size"), &TileMapPattern::remove_cell);
	ClassDB::bind_method(D_METHOD("get_cell_source_id", "coords"), &TileMapPattern::get_cell_source_id);
	ClassDB::bind_method(D_METHOD("get_cell_atlas_coords", "coords"), &TileMapPattern::get_cell_atlas_coords);
	ClassDB::bind_method(D_METHOD("get_cell_alternative_tile", "coords"), &TileMapPattern::get_cell_alternative_tile);
	ClassDB::bind_method(D_METHOD("get_used_cells"), &TileMapPattern::get_used_cells);
	ClassDB::bind_method(D_METHOD("get_size"), &TileMapPattern::get_size);
	ClassDB::bind_method(D_METHOD("set_size", "size"), &TileMapPattern::set_size);
	ClassDB::bind_method(D_METHOD("is_empty"), &TileMapPattern::is_empty);
}
bool TileSet::TerrainsPattern::is_valid() const {
	return valid;
}
bool TileSet::TerrainsPattern::is_erase_pattern() const {
	return not_empty_terrains_count == 0;
}
bool TileSet::TerrainsPattern::operator<(const TerrainsPattern &p_terrains_pattern) const {