Enable EntityRef tests that now pass. (#16263)

# Objective

Re-enable some tests in `entity_ref.rs` that are marked as `#[ignore]`,
but that pass after #14561.

## Solution

Remove `#[ignore]` from those tests.

Author: chescock

crates/bevy_ecs/src/world/entity_ref.rs

@@ -4036,7 +4036,6 @@ mod tests {
     }
 
     #[test]
-    #[ignore] // This should pass, but it currently fails due to limitations in our access model.
     fn ref_compatible_with_resource_mut() {
         fn borrow_system(_: Query<EntityRef>, _: ResMut<R>) {}
 
@@ -4067,15 +4066,13 @@ mod tests {
     }
 
     #[test]
-    #[ignore] // This should pass, but it currently fails due to limitations in our access model.
     fn mut_compatible_with_resource() {
         fn borrow_mut_system(_: Res<R>, _: Query<EntityMut>) {}
 
         assert_is_system(borrow_mut_system);
     }
 
     #[test]
-    #[ignore] // This should pass, but it currently fails due to limitations in our access model.
     fn mut_compatible_with_resource_mut() {
         fn borrow_mut_system(_: ResMut<R>, _: Query<EntityMut>) {}