HOTFIX update member activity migration to handle deleted users

[JeffreyThiessen]

What does this PR do and why?

Describe in detail what your merge request does and why.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. checkout irida next from a git hash before the migration, build db

git checkout 6facd06a29c38cdb80012367dcf7dbc07a250a5d

./scripts/clean_dev.sh

2. run irida next
3. create a new user "myuser"
4. sign out
5. sign in with admin
6. create a new group/project
7. add "myuser" to group/project
8. sign out of admin
9. sign in with "myuser"
10. delete "myuser" from edit profile page
11. sign in with admin
12. check that user "myuser" is no longer a member of group/project
13. checkout this PR branch and migrate

git checkout hotfix_member_activity_migration

rails db:migrate

14. Migration should succeed
15. run irida next and view the activity page for the group/project we used previously. Activity should sat "Deleted User" for activities associated with now deleted "myuser"

PR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the PR acceptance checklist for this PR.

[github-actions]

Code Metrics Report

Coverage	Test Execution Time
93.2%	11m17s

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Reported by octocov

[ChrisHuynh333]

Works as described, thanks for fixing this.

[joshsadam]

This looks really good to me as well.  Agree, that it works as advertised.