8884: fix: add_explicit_type produces invalid code on `@` patterns r=Veykril a=iDawer
In
```rust
let name @ () = ();
```
an explicit type should be inserted after the pattern, not just after the name.
`let` statement defined as `LetStmt = Attr* 'let' Pat (':' Type)? '=' initializer:Expr ';'`
Co-authored-by: Dawer <7803845+iDawer@users.noreply.github.com>
2d76b176c0