avm2: Preserve attribute flag when filling lazy multiname with QName

Fixes #12570

core/src/avm2/multiname.rs

@@ -253,8 +253,13 @@ impl<'gc> Multiname<'gc> {
                 if self.has_lazy_ns() {
                     let _ = activation.pop_stack(); // ignore the ns component
                 }
-                let name = qname_object.name();
+                let mut name = qname_object.name().clone();
-                return Ok(name.clone());
+
+                if self.is_attribute() {
+                    name.set_is_attribute(true);
+                }
+
+                return Ok(name);
             }
 
             Some(name_value.coerce_to_string(activation)?)

tests/tests/swfs/avm2/qname_as_lazy_name_attribute_multiname/Test.as

@@ -0,0 +1,18 @@
+package
+{
+    import flash.display.Sprite;
+
+    public class Test extends Sprite
+    {
+    }
+}
+
+var xml =
+    <alpha>
+    <bravo attr1="value1" attr2="wrong">
+        <charlie attr1="value2" attr2="wrong"/>
+    </bravo>
+</alpha>;
+
+var q = new QName("attr1");
+trace("xml..@[q]: " + xml..@[q]);

tests/tests/swfs/avm2/qname_as_lazy_name_attribute_multiname/output.txt

@@ -0,0 +1 @@
+xml..@[q]: value1value2

tests/tests/swfs/avm2/qname_as_lazy_name_attribute_multiname/test.toml

@@ -0,0 +1 @@
+num_ticks = 1