Meeting invitations bugfix: don’t count invitations to prior meetings as duplicates for bulk invites to a new meeting

@DSASanFrancisco/portal-members

SUMMARY

jeffmay 9:46 PM I think something is wrong with the bulk invite feature for the meetings on the membership portal on prod it isn’t working for the Tech Committee meeting I set up

The issue was that we invited everyone to last week's meeting, and the prevent-duplicate-invites code wasn't noticing that the invites were to separate meetings. Altered that query, and added a test case to confirm.