[projects] fix project association for workspaces based on prebuilds

[AlexTugarev]

Description

A follow-up to #6097

Related Issue(s)

Fixes #6116

How to test

1. create a team and a project with prebuilds configured.
2. create a prebuild
3. with another account (not a member of the same team) try to start a workspace for the repo from 1.)
4. see that the workspace is shown in the personal space (/workspaces)

Release Notes

[Dashboard] Fix workspace-project associations for workspaces based on prebuilds.

[AlexTugarev]

@jankeromnes try with https://at-fix-project-association.staging.gitpod-dev.com/#https://gitlab.com/AlexTugarev/create-react-app/-/tree/main

[jankeromnes]

Many thanks for the quick fix! 🎉

Code change looks good and works like a charm. ❇️

[roboquat]

LGTM label has been added.

Git tree hash: fe72a611f630409e317e935a91b77a109473a900

[roboquat]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jankeromnes

Associated issue: #6116

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