Change ref and ref! to unary operators

compiler/erg_parser/lex.rs

@@ -525,6 +525,8 @@ impl Lexer /*<'a>*/ {
             "isnot" => IsNotOp,
             "dot" => DotOp,
             "cross" => CrossOp,
+            "ref" => RefOp,
+            "ref!" => RefMutOp,
             // これらはリテラルというより定数だが便宜的にリテラルということにしておく
             "True" | "False" => BoolLit,
             "None" => NoneLit,