Auto format let-else block (#10214)

<!--
if this PR closes one or more issues, you can automatically link the PR
with
them by using one of the [*linking
keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword),
e.g.
- this PR should close #xxxx
- fixes #xxxx

you can also mention related issues, PRs or discussions!
-->

# Description
<!--
Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.

Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.
-->
rustfmt 1.6.0 has added support for formatting [let-else
statements](https://doc.rust-lang.org/rust-by-example/flow_control/let_else.html)

See https://github.com/rust-lang/rustfmt/blob/master/CHANGELOG.md#added

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

# 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` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# 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-parser/src/parse_keywords.rs

@@ -3510,7 +3510,7 @@ pub fn parse_register(working_set: &mut StateWorkingSet, spans: &[Span]) -> Pipe
                 value_as_string(val, expr.span).map_err(|err| err.wrap(working_set, call.head))?;
 
             let Some(path) = find_in_dirs(&filename, working_set, &cwd, PLUGIN_DIRS_VAR) else {
-                return Err(ParseError::RegisteredFileNotFound(filename, expr.span))
+                return Err(ParseError::RegisteredFileNotFound(filename, expr.span));
             };
 
             if path.exists() && path.is_file() {