Shadow rs dep (#8298)

# Description

While looking at the recent MR merged, I noticed that a dependency was
no more used with https://github.com/nushell/nushell/pull/8280.

# User-Facing Changes

None.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-cmd-lang/Cargo.toml

@@ -22,10 +22,10 @@ nu-utils = { path = "../nu-utils", version = "0.76.1" }
 fancy-regex = "0.11.0"
 itertools = "0.10.0"
 log = "0.4.14"
-shadow-rs = { version = "0.20.0", default-features = false }
+shadow-rs = { version = "0.21.0", default-features = false }
 
 [build-dependencies]
-shadow-rs = { version = "0.20.0", default-features = false }
+shadow-rs = { version = "0.21.0", default-features = false }
 
 [dev-dependencies]
 nu-test-support = { path="../nu-test-support", version = "0.76.1"  }