backport fix for thumbnails rendering issue

[martint-unity]

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Purpose of this PR

backport of this #5778
here is the FB case https://fogbugz.unity3d.com/f/cases/1367634/

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Testing status

Tested by manually import all and see that the backgrounds now are fixed for the thumbnails.
Running Yamato

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Comments to reviewers

Notes for the reviewers you have assigned.

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
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URP
/.yamato%252Fall-urp.yml%2523PR_URP_2021.2

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[github-actions]

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[erikabar]

looks good, approved without additional testing