Properly set GDExtensionBool is_valid to true in to_string function.#1145

Bromeon merged 2 commits intogodot-rust:mastergodot-rust/gdext:masterfrom

Yarwin:bugfix-set-is-valid-in-to-stringYarwin/gdext:bugfix-set-is-valid-in-to-stringCopy head branch name to clipboard