Don't fail while fetching remediations from a removed artifact

Mehmet Emin INACrequested to merge
390085_dont_fail_to_fetch_remediation_when_the_artifact_is_removed into master

What does this MR do and why?

Artifacts can be removed from the system manually by the users so we need to take this into account while trying to read the remediations from the artifacts.

Related to Security::Finding#remediations raises an except... (#390085 - closed).

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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