Change camera order ambiguity warning to warn_once! (#22649)

## Objective

Fixes #22635

Camera order ambiguity warnings currently fire every frame, flooding the
console.

## Solution

- Change `warn!` to `warn_once!` in `sort_cameras` so the warning only
fires once per ambiguity
- Remove the log filter workaround from `ui_target_camera` example since
the warning is no longer spammy

## Testing

Ran the `ui_target_camera` example and triggered a camera order
ambiguity by clicking to give two cameras the same order. Verified the
warning appears exactly once in the logs despite running for many frames
afterward.

---------

Co-authored-by: Alice Cecile <[email protected]>

Author: natepiano

crates/bevy_render/src/camera.rs

@@ -41,6 +41,7 @@ use bevy_ecs::{
 };
 use bevy_image::Image;
 use bevy_log::warn;
+use bevy_log::warn_once;
 use bevy_math::{uvec2, vec2, Mat4, URect, UVec2, UVec4, Vec2};
 use bevy_platform::collections::{HashMap, HashSet};
 use bevy_reflect::prelude::*;
@@ -652,7 +653,7 @@ pub fn sort_cameras(
     }
 
     if !ambiguities.is_empty() {
-        warn!(
+        warn_once!(
             "Camera order ambiguities detected for active cameras with the following priorities: {:?}. \
             To fix this, ensure there is exactly one Camera entity spawned with a given order for a given RenderTarget. \
             Ambiguities should be resolved because either (1) multiple active cameras were spawned accidentally, which will \

examples/ui/ui_target_camera.rs

@@ -4,17 +4,11 @@ use bevy::color::palettes::css::BLUE;
 use bevy::color::palettes::css::GREEN;
 use bevy::color::palettes::css::RED;
 use bevy::color::palettes::css::YELLOW;
-use bevy::log::LogPlugin;
-use bevy::log::DEFAULT_FILTER;
 use bevy::prelude::*;
 
 fn main() {
     App::new()
-        .add_plugins(DefaultPlugins.set(LogPlugin {
-            // Disable camera order ambiguity warnings
-            filter: format!("{DEFAULT_FILTER},bevy_render::camera=off"),
-            ..Default::default()
-        }))
+        .add_plugins(DefaultPlugins)
         .add_systems(Startup, setup)
         .run();
 }