Enable clippy::option_map_unit_fn (#8751)

This PR enables the
[`clippy::option_map_unit_fn`](https://rust-lang.github.io/rust-clippy/master/index.html#/option_map_unit_fn)
rule and fixes the outstanding violations.

Release Notes:

- N/A

tooling/xtask/src/main.rs

@@ -108,7 +108,6 @@ fn run_clippy(args: ClippyArgs) -> Result<()> {
         "clippy::non_canonical_clone_impl",
         "clippy::non_canonical_partial_ord_impl",
         "clippy::nonminimal_bool",
-        "clippy::option_map_unit_fn",
         "clippy::redundant_closure_call",
         "clippy::redundant_guards",
         "clippy::reversed_empty_ranges",