Downgrade gpu_readback closed-channel log from warn to debug

[PeteMichaud]

map_async callbacks in map_buffers fire during wgpu's shutdown device-poll, after GpuReadbacks (which owns the channel receivers) has already been dropped. The try_send fails with Closed — expected, since the consumer is gone because the app is exiting. The same happens when a Readback entity is intentionally despawned.

This produces two WARN bevy_render::gpu_readback: Failed to send readback result: ... lines on every app exit for any app using Readback. The warning is never actionable.

Downgrade to debug! so the message is still available for diagnosis but doesn't pollute default log output.

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[PeteMichaud]

Context for me here is that I wanted to stop this from spamming my console and I realized that it was either a tiny change here that I believe everyone who uses readback would want, or some huge song and dance of forking or vendoring just this or something crazy.

[alice-i-cecile]

Context for me here is that I wanted to stop this from spamming my console and I realized that it was either a tiny change here that I believe everyone who uses readback would want, or some huge song and dance of forking or vendoring just this or something crazy.

FYI you can filter logs :) Still, I agree with this downgrade!