Resolve needless_borrow pedantic clippy lint in test

    error: the borrowed expression implements the required traits
        --> tests/test.rs:1931:34
         |
    1931 |     assert!(serde_json::to_value(&map).is_err());
         |                                  ^^^^ help: change this to: `map`
         |
         = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
         = note: `-D clippy::needless-borrow` implied by `-D clippy::all`

Author: dtolnay

tests/test.rs

@@ -1928,7 +1928,7 @@ fn test_deny_float_key() {
 
     // map with float key
     let map = treemap!(Float => "x");
-    assert!(serde_json::to_value(&map).is_err());
+    assert!(serde_json::to_value(map).is_err());
 }
 
 #[test]