Fix new clippy lint (rust 1.74.0)

[rkuris]

error: unnecessary map on constructor Some(_)
--> firewood/src/merkle.rs:1612:21
|
1612 | let value = Some(value).map(Data);
| ^^^^^^^^^^^^^^^^^^^^^ help: try: Some(Data(value))
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_map_on_constructor
= note: -D clippy::unnecessary-map-on-constructor implied by -D warnings
= help: to override -D warnings add #[allow(clippy::unnecessary_map_on_constructor)]

Checking fwdctl v0.0.4 (/home/runner/work/firewood/firewood/fwdctl)

error