"Shared Submissions" feature on MyDSpace is sharing too many submissions

[tdonohue]

Describe the bug

This issue was found during testing of #5145, the PR which adds this new "Shared Submissions" option to Collections and MyDSpace.

When visiting the "Shared Submissions" option in a user's MyDSpace page, submissions which are not shared also appear in the list.

To Reproduce

Steps to reproduce the behavior:

1. Login as an Admin
2. Create a single Collection with the "Shared Workspace" option enabled.
3. Add one other user as a Submitter to that Collection (you'll use this user later)
4. Start one submission into that Collection. Save it for later.
5. Logout and login as the Submitter you created in step 3
6. Go to that user's MyDSpace page and select "Shared Submissions" from the dropdown.
7. You should only see one shared submission (the one started in step 4). However, you will see many more than expected. (It almost appears like every in progress submission from the Admin user has been shared)
8. Even worse it appears that it's possible to edit any of the "Shared Submissions". So, you've been given access to edit Submissions that you should not be allowed to access.

Expected behavior

Obviously, you should only be able to see/edit shared submissions which belong to a "Shared Workspace" collection.

Related work

This "Shared Submissions" feature was introduced in #5145.

[tdonohue]

Discussed in the Merger Management Team meeting today.

@abollini asked to be assigned to this as he wasn't aware of this issue and wanted to investigate it further.

I mentioned I would add more context about this issue as well.

• It was originally reported in this review from me.
• In the next comment, @FrancescoMolinaro mentioned they were looking into it.
• The issue was also reported/seconded by @alexandrevryghem in this later comment.

This ticket remains a blocker for 10.0.