fix outline issue: allow Ref in Math in latex.grammar (#13054)

* added failing test

* latex.grammar update: allow Ref in Math

GitOrigin-RevId: 340bf40cf4804e7693965a29b16b869a54a467d7

services/web/frontend/js/features/source-editor/lezer-latex/latex.grammar

@@ -628,6 +628,9 @@ Math {
     | Label {
         LabelCtrlSeq optionalWhitespace? OptionalArgument? LabelArgument
     }
+    | Ref {
+        (RefCtrlSeq | RefStarrableCtrlSeq "*"?) optionalWhitespace? OptionalArgument? optionalWhitespace? OptionalArgument? optionalWhitespace? RefArgument
+    }
     )+
 }