Fix cargo b -p nu-command --tests (#11939)

The feature `sqlite` is not active by default on `nu-command`.
Only when building `cargo b --all --tests` would the feature be
activated via `nu`'s feature requirements.

Make the tests conditional

Saw this when double checking the removals from #11938.
Making sure each crate still compiles individually, ensures both that
you can run subcrate tests independently and that the `cargo publish`
run will succeed to build the crate with the default feature set (see
the problems occurring for the `0.90.0` release.

crates/nu-command/tests/commands/mod.rs

@@ -13,6 +13,7 @@ mod config_nu_default;
 mod continue_;
 mod conversions;
 mod cp;
+#[cfg(feature = "sqlite")]
 mod database;
 mod date;
 mod debug_info;