Remove redundant BasicLabel cloning in parser TokenTree rule (#9486)

Author: conomist

crates/cairo-lang-sierra/src/parser.lalrpop

@@ -99,7 +99,7 @@ TokenTree: String = {
     <value:BracesTokenTree> => value,
     <value:BracketsTokenTree> => value,
     "(" <parts:(<TokenTree>)*> ")" => format!("({})", parts.join("")),
-    <label:BasicLabel> => label.to_string(),
+    <label:BasicLabel> => label,
     <num:BigInt> => num.to_string(),
     ":" => <>.to_string(),
     "," => <>.to_string(),