Ignore PipelineCache ambiguities (bevyengine#14772)

# Objective

The `prepare_view_upscaling_pipelines` system has dozens of ambiguities,
which makes it harder to spot and prevent new ambiguities.

Closes bevyengine#14770.

## Solution

Just exclude the system from ambiguity detection. See the linked issue
for more context on why this resolution was chosen.

## Testing

Running the `ambiguity_detection` example now reports dozens fewer
`Render` app ambiguities.

crates/bevy_core_pipeline/src/upscaling/mod.rs

@@ -17,7 +17,14 @@ impl Plugin for UpscalingPlugin {
         if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
             render_app.add_systems(
                 Render,
-                prepare_view_upscaling_pipelines.in_set(RenderSet::Prepare),
+                // This system should probably technically be run *after* all of the other systems
+                // that might modify `PipelineCache` via interior mutability, but for now,
+                // we've chosen to simply ignore the ambiguities out of a desire for a better refactor
+                // and aversion to extensive and intrusive system ordering.
+                // See https://github.com/bevyengine/bevy/issues/14770 for more context.
+                prepare_view_upscaling_pipelines
+                    .in_set(RenderSet::Prepare)
+                    .ambiguous_with_all(),
             );
         }
     }