Fixed: Default window is now "App" instead of "Bevy App" (#9301)

# Objective

Fixes #9298 - Default window title leaks "bevy" context

## Solution

I just replaced the literal string "Bevy App" with "App" in Window's
Default trait implementation.

crates/bevy_window/src/window.rs

@@ -217,7 +217,7 @@ pub struct Window {
 impl Default for Window {
  fn default() -> Self {
  Self {
- title: "Bevy App".to_owned(),
+ title: "App".to_owned(),
  cursor: Default::default(),
  present_mode: Default::default(),
  mode: Default::default(),