derived Debug on EventReader (#6600)

# Objective
Fixes #6588 

## Solution

Added Debug to the derived traits of EventReader.

crates/bevy_ecs/src/event.rs

@@ -184,7 +184,7 @@ impl<E: Event> DerefMut for EventSequence<E> {
 }
 
 /// Reads events of type `T` in order and tracks which events have already been read.
-#[derive(SystemParam)]
+#[derive(SystemParam, Debug)]
 pub struct EventReader<'w, 's, E: Event> {
     reader: Local<'s, ManualEventReader<E>>,
     events: Res<'w, Events<E>>,