Try despawning the related Observer from ObservedBy.

[andriyDev]

Objective

• Fixes Despawning observers through its target after despawning through another Relationship logs a warning! #24700

Solution

• Switch despawn to try_despawn.
  • It looks like this happens if the relationship despawns the observer, and then the ObservedBy tries to despawn the observer.

Testing

• Ran the example in Despawning observers through its target after despawning through another Relationship logs a warning! #24700. No more warning!
• I couldn't really add a test for this because testing logging is kinda difficult.

[mgi388]

Approving on the basis that I’ve had this patch in my Bevy 0.18 fork for ages: mgi388@f2ebb13

I’ve tried to wrap my head around the deferred nature of Bevy in cases like this. And I’ve just come to the conclusion that most things like this are deferred, as in something else could have removed the entity by the time the despawn here actually runs so I feel like all of these need to be try_. Not an ECS dev though.