[docs] devtools example errors in v2

[Stefan Grönke]

Documented on: https://beta.tauri.app/guides/debug/application/#opening-devtools-programmatically

lib.rs

use tauri::Manager;

#[cfg_attr(mobile, tauri::mobile_entry_point)]
pub fn run() {
  tauri::Builder::default()
    .setup(|app| {
      #[cfg(debug_assertions)] // only include this code on debug builds
      {
        let window = app.get_window("main").unwrap();
        window.open_devtools();
        window.close_devtools();
      }
      Ok(())
    })
    .run(tauri::generate_context!())
    .expect("error while running tauri application");
}

% cargo tauri dev
...
warning: unused import: `tauri::Manager`
 --> src/lib.rs:1:5
  |
1 | use tauri::Manager;
  |     ^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error[E0599]: no method named `get_window` found for mutable reference `&mut tauri::App` in the current scope
 --> src/lib.rs:9:26
  |
9 |         let window = app.get_window("main").unwrap();
  |                          ^^^^^^^^^^ method not found in `&mut App`

For more information about this error, try `rustc --explain E0599`.
warning: `app` (lib) generated 1 warning
error: could not compile `app` (lib) due to 1 previous error; 1 warning emitted

[Vitor Ayres]

thanks for reporting @gronke, should be solved with the mentioned PR.