Add test for nested box pattern

Author: ecstatic-morse

crates/ra_syntax/test_data/parser/inline/ok/0066_match_arm.rs

@@ -5,5 +5,7 @@ fn foo() {
         X | Y if Z => (),
         | X | Y if Z => (),
         | X => (),
+        box X => (),
+        Some(box X) => (),
     };
 }