Disable question_mark clippy lint in lexical test

Serde_json uses #![deny(clippy::question_mark_used)].

    warning: this `match` expression can be replaced with `?`
      --> tests/../src/lexical/algorithm.rs:54:21
       |
    54 |           let value = match mantissa.checked_mul(power) {
       |  _____________________^
    55 | |             None => return None,
    56 | |             Some(value) => value,
    57 | |         };
       | |_________^ help: try instead: `mantissa.checked_mul(power)?`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#question_mark
       = note: `-W clippy::question-mark` implied by `-W clippy::all`
       = help: to override `-W clippy::all` add `#[allow(clippy::question_mark)]`

tests/lexical.rs

@@ -12,6 +12,7 @@
     clippy::let_underscore_untyped,
     clippy::module_name_repetitions,
     clippy::needless_late_init,
+    clippy::question_mark,
     clippy::shadow_unrelated,
     clippy::similar_names,
     clippy::single_match_else,