Fix bevy_app not compiling without default features (#13532)

# Objective

Fix #13530 (just realized creating an issue was unnecessary since it's a
super simple fix)

## Solution

Add a cfg feature attribute

## Testing

Compiles fine now

Author: ItsDoot

crates/bevy_app/src/main_schedule.rs

@@ -175,6 +175,7 @@ impl Default for MainScheduleOrder {
             labels: vec![
                 First.intern(),
                 PreUpdate.intern(),
+                #[cfg(feature = "bevy_state")]
                 StateTransition.intern(),
                 RunFixedMainLoop.intern(),
                 Update.intern(),