prevent crash when use redirection with let/mut (#10139)

Fix #9992 

I mistakenly messed up https://github.com/nushell/nushell/pull/10118 and
this is a cleaned version.

# Description

* This pr changes the panic to errors while parsing `let`, now user will
get the following errors:
<img width="395" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/4b39ac14-cd1f-47b3-9490-81009ca42717">
<img width="394" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/71ce33ad-f4d0-4132-828f-9674b9603556">
<img width="440" alt="scr"
src="https://github.com/nushell/nushell/assets/1991933/257eab4d-1a72-42db-b09e-f42bef33d2ec">

* `out+err>` is cached by `parse_expression` but not this, which may be
a potential problem.
* `Commond(None, ..)` remains panic for future bug report because I
don't actually know when/how does it happen

# User-Facing Changes

Nushell won't crash when user typing `let a = 1 err> ...`

# Tests + Formatting

- `cargo fmt --all -- --check` : OK
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` : OK
- `cargo test --workspace` : OK
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` : OK

# After Submitting

None

Co-authored-by: Horasal <horsal@horsal.dev>

crates/nu-protocol/src/parse_error.rs

@@ -466,6 +466,13 @@ pub enum ParseError {
         #[label("{label}")]
         span: Span,
     },
+
+    #[error("Redirection can not be used with let/mut.")]
+    #[diagnostic()]
+    RedirectionInLetMut(
+        #[label("Not allowed here")] Span,
+        #[label("...and here")] Option<Span>,
+    ),
 }
 
 impl ParseError {
@@ -550,6 +557,7 @@ impl ParseError {
             ParseError::UnknownOperator(_, _, s) => *s,
             ParseError::InvalidLiteral(_, _, s) => *s,
             ParseError::LabeledErrorWithHelp { span: s, .. } => *s,
+            ParseError::RedirectionInLetMut(s, _) => *s,
         }
     }
 }