Fix exit code of --help and --version, and test them in CI

Corrects prior regression which caused ERROR output and exit code of 1.

platform/linuxbsd/godot_linuxbsd.cpp

@@ -61,6 +61,10 @@ int main(int argc, char *argv[]) {
 	Error err = Main::setup(argv[0], argc - 1, &argv[1]);
 	if (err != OK) {
 		free(cwd);
+
+		if (err == ERR_HELP) { // Returned by --help and --version, so success.
+			return 0;
+		}
 		return 255;
 	}