Support UTF-8 input action names

Fixes #26380

(cherry picked from commit a7430a9d060614169dd00117adc00ffab2a245a7)

core/variant_parser.cpp

@@ -1542,6 +1542,9 @@ Error VariantParser::parse_tag_assign_eof(Stream *p_stream, int &line, String &r
 			} else if (c != '=') {
 				what += String::chr(c);
 			} else {
+				if (p_stream->is_utf8()) {
+					what.parse_utf8(what.ascii(true).get_data());
+				}
 				r_assign = what;
 				Token token;
 				get_token(p_stream, token, line, r_err_str);