Use {} instead of explicit return

Clippy emits:

 warning: unneeded `return` statement

It is more conventional to use `{}` and not an explicit `return`
statement.

Author: tcharding

src/miniscript/mod.rs

@@ -606,7 +606,7 @@ mod tests {
                 assert_eq!(ms.ty.mall.safe, need_sig);
                 assert_eq!(ms.ext.ops.op_count().unwrap(), ops);
             }
-            (Err(_), false) => return,
+            (Err(_), false) => {}
             _ => unreachable!(),
         }
     }