uucore: locale: Use if let instead of match

[drinkcat]

Recent cargo clippy prefers to use if let for single pattern.

For some reason it only triggers on one of the LANG restore case though, but we can just fix them all.

Not completely sure why cargo clippy only complains about this one:

error: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
   --> src/uucore/src/lib/mods/locale.rs:767:9
    |
767 | /         match original_lang {
768 | |             Some(val) => unsafe {
769 | |                 env::set_var("LANG", val);
770 | |             },
771 | |             None => {} // Was already unset
772 | |         }
    | |_________^
    |
    = note: you might want to preserve the comments from inside the `match`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_match
    = note: `-D clippy::single-match` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::single_match)]`
help: try
    |
767 ~         if let Some(val) = original_lang { unsafe {
768 +             env::set_var("LANG", val);
769 +         } }
    |

@sylvestre FYI

[cakebaker]

clippy probably complains because the comment is outside the block.

[drinkcat]

clippy probably complains because the comment is outside the block.

You are correct! That would have fixed it too...

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)