tryfix(16459): xml literal in for comprehension

xml literal may appear in LHS of for comprehension.

The previous fix caused a syntax error for the following code.

```scala
val actual: List[Node] = for (case t @ <book><title>Blabla</title></book> <- NodeSeq.fromSeq(books.child).toList)
  yield t
```

Author: i10416

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -906,7 +906,7 @@ object Parsers {
       var braces = 0
       while (true) {
         val token = lookahead.token
-        if (token == XMLSTART) return false
+        if (query != LARROW && token == XMLSTART) return false
         if (braces == 0) {
           if (token == query) return true
           if (stopScanTokens.contains(token) || lookahead.isNestedEnd) return false