Direct transfer will match incorrect user for activity items

Summary

When using direct transfer, even with otherwise correctly set up user matching, activity items will match unrelated users.

Steps to reproduce

1. GitLab.com Have two different users:
   • User1, with primary email address EmailA
   • User2, with primary email address EmailB
2. Self-managed instance Have a user named User1 with primary/public email address EmailB
3. Self-managed instance Let User1 create an issue and assign to themselves
4. GitLab.com Direct transfer the self-managed group housing the project from step 3 to GitLab.com
5. GitLab.com Observe that:
   • The issue is assigned correctly: It is assigned to User2 as per the match on EmailB
   • In the activity history of the issue an item will state that User2 has assigned the issue to User1

Example Project

This issue showcases the behavior: test3390922/export-this/test#1 – the activity item says that the issue was assigned to my normal account, @manuelgrabowski. The issue is actually (and correctly!) assigned to my admin account @manuelgrabowski-admin:

In my self-hosted test intance, the account has the @manuelgrabowski username, but the same public email as the @manuelgrabowski-admin account on GitLab.com:

What is the current bug behavior?

Activity item doesn't match correct user

What is the expected correct behavior?

Activity item does match correct user

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

The self-managed source instance I reproduced this with is running v16.0.1-ee, customer (internal) is experiencing the problem with 15.8.5.

Results of GitLab application Check

Possible fixes