Fix lexer behavior on non-whitespace before ref (#4553)

crates/typst-syntax/src/lexer.rs

@@ -474,7 +474,7 @@ impl Lexer<'_> {
                 Some('-') if !s.at(['-', '?']) => {}
                 Some('.') if !s.at("..") => {}
                 Some('h') if !s.at("ttp://") && !s.at("ttps://") => {}
-                Some('@') if !s.at(is_id_start) => {}
+                Some('@') if !s.at(is_valid_in_label_literal) => {}
                 _ => break,
             }
 

tests/suite/model/ref.typ

@@ -54,3 +54,8 @@ $ A = 1 $ <eq2>
 // Error: 1-7 label occurs in the document and its bibliography
 @arrgh
 #bibliography("/assets/bib/works.bib")
+
+--- issue-4536-non-whitespace-before-ref ---
+// Test reference with non-whitespace before it.
+#figure[] <1>
+#test([(#ref(<1>))], [(@1)])