`Observer`s' underlying system state can change after they have been spawned

## Bevy version and features

https://github.com/bevyengine/bevy/commit/69745d40e594fb34a99507e2f0be2385711e46a6 but also likely 0.16.1

## What you did

```rs
use bevy_ecs::{entity_disabling::Internal, prelude::*, system::IntoObserverSystem};

fn main() {
#[derive(EntityEvent)]
struct Ev;

struct Local1(&'static i32);

impl Default for Local1 {
fn default() -> Self {
Local1(&0)
}
}

#[derive(Default)]
struct Local2(usize);

fn bad_observer(_: On, local: Local) {
println!("{}", local.0);
}

let mut world = World::new();

world.add_observer(bad_observer);

let mut s = IntoObserverSystem::into_system(|_: On, _: Local| {});
s.initialize(&mut world);

*world
.query_filtered::<&mut Observer, With>()
.single_mut(&mut world)
.unwrap() = Observer::new(s);

world.trigger(Ev);
}
```

## What went wrong

This causes a segfault in release mode, because the original system is run with the new system's local, effectively transmuting the local's type.

In debug mode it fails the following assertion:

https://github.com/bevyengine/bevy/blob/69745d40e594fb34a99507e2f0be2385711e46a6/crates/bevy_ecs/src/observer/runner.rs#L56

This is similar to #20736 in that both are caused by the `Observer` component being replaced, however it's different in that it doesn't need the observer to be currenlty running, so a fix that just temporarily moves out the system state while running won't fix this issue too.