Force floats to output a decimal in nuon (#5768)

* Force floats to output a decimal in nuon

* Add test

crates/nu-command/tests/format_conversions/nuon.rs

@@ -190,3 +190,15 @@ fn read_bool() {
 
     assert_eq!(actual.out, "true")
 }
+
+#[test]
+fn float_doesnt_become_int() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            1.0 | to nuon
+        "#
+    ));
+
+    assert_eq!(actual.out, "1.0")
+}