Fix slack once and for all (#946)

The red X keeps coming back so I'd like to mark this as allowably fail-able -- that way the innards of Slack/OAuth/Tableau credentials don't keep polluting test run reports :)

Author: t8y8

.github/workflows/slack.yml

@@ -4,6 +4,7 @@ on: [push, pull_request, issues]
 
 jobs:
   slack-notifications:
+    continue-on-error: true
     runs-on: ubuntu-20.04
     name: Sends a message to Slack when a push, a pull request or an issue is made
     steps: