[admin] Fix adminRestoreSoftDeletedWorkspace

[corneliusludmann]

The “Restore & Pin” link in the admin portal does not work. This PR fixes the rights check.

How to test

1. Login with a user A. This user is the admin user.
2. Login in another session (e.g. incognito window) with another user B. This user is a normal user.
3. Start & stop a workspace with user B. Delete this workspace.
4. Look for this workspace in the admin dashboard with user A. There should be a “Restore & Pin” link. Click it!
5. Verify that the “Soft Deleted” column updates to “No” immediately for user A.
6. Verify that user B has the workspace in the list of active workspaces (pinned).

It's important to do this with 2 users because in the previous implementation the problem was, that you can restore your own workspace only (due to the rights check).

Fixes #4583

[geropl]

/werft run

👍 started the job as gitpod-build-clu-fix-admin-restore-and-pin.4

[geropl]

Tested, works as advertised.

A small reminder in favor of integration tests: large parts of the test could be automated. Don't want to block the PR, just to nag a bit 🙃