Fix emissive color when switching from ldr to HDR

[adrien-de-tocqueville]

Purpose of this PR

the fix was included in the PR #5761. We can't backport all the PR so that's just the fix

[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.
Link to Yamato: https://yamato.cds.internal.unity3d.com/jobs/902-Graphics
Search for your PR branch using the sidebar on the left, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

HDRP
/.yamato%252Fall-hdrp.yml%2523PR_HDRP_2021.2

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[github-actions]

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