chore: fix body expr span

[ghost]

Description

before:

error: expected type Field, found type ()
  ┌─ /app/src/main.nr:1:4
  │
1 │ fn main() -> Field {
  │    ----      ----- expected Field because of return type
  │    │          
  │    () returned here
  │

after:

error: expected type Field, found type ()
  ┌─ /app/src/main.nr:1:14
  │  
1 │   fn main() -> Field {
  │                ----- expected Field because of return type
  │ ╭────────────────────'
2 │ │     let n = 3;
3 │ │     let n2 = 5;
4 │ │ 
5 │ │     
6 │ │ }
  │ ╰─' () returned here
  │  

Problem

#2302 (comment)

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[jfecher]

Thank you!