Fix volume annotation downsampling

[fm3]

getFallbackLayer queries the dataset info from wk by the tracingId. But since downsampling is part of the duplicate route, the new tracingId is not yet known by the wk side. However, the fallback layer should not change in the duplicate, so using the old id is valid.

Steps to test:

• Create volume annotation with resolution restriction, brush some (multiple sections)
• Hit downsample button in the sidebar, confirm
• Should work, yield valid annotation

Issues:

• fixes Downsampling of volume annotation is broken #7758

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• Updated changelog