Fix deletion of deploy keys linked to other projects
What does this MR do?
When a project is deleted, this MR ensures that we don't delete its deploy keys if they are linked to other projects.
Why was this MR needed?
https://gitlab.com/gitlab-org/gitlab-ce/issues/35630
Does this MR meet the acceptance criteria?
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Changelog entry added, if necessary -
Documentation created/updated -
API support added - Tests
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Added for this feature/bug -
All builds are passing
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- Review
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Has been reviewed by UX -
Has been reviewed by Frontend -
Has been reviewed by Backend -
Has been reviewed by Database
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Conform by the merge request performance guides -
Conform by the style guides -
Branch has no merge conflicts with master
(if it does - rebase it please) -
Squashed related commits together
What are the relevant issue numbers?
Fixes #35630