fix(slack-notifications): [nan-1164] dedupe slack notifications

[khaliqgant]

Describe your changes

In an auth scenario we actually weren't deduping notifications but rather incrementing the count which doesn't make sense for an auth connection failure. Adjust logic for auth if it already has an open notification then we bail

Issue ticket number and link

NAN-1164

Checklist before requesting a review (skip if just adding/editing APIs & templates)

• [ ] I added tests, otherwise the reason is:
• [ ] I added observability, otherwise the reason is:
• [ ] I added analytics, otherwise the reason is:

[linear[bot]]

NAN-1164 Credal Box connection failing to refresh intermittently