Update Slack user group for a schedule - handle `paid_team_only` Slack API error #947

Job	Run time
Linting and tests / Lint database migrations	1m 22s
Linting and tests / Lint entire project	2m 52s
Linting and tests / Lint, test, and build frontend	1m 52s
Linting and tests / mypy	2m 10s
Linting and tests / Test technical documentation	16s
Linting and tests / Backend Tests: MySQL + RabbitMQ (RBAC enabled: True)	3m 26s
Linting and tests / Backend Tests: SQLite + Redis (RBAC enabled: True)	3m 7s
Linting and tests / Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: True)	3m 42s
Linting and tests / Backend Tests: MySQL + RabbitMQ (RBAC enabled: False)	2m 57s
Linting and tests / Backend Tests: SQLite + Redis (RBAC enabled: False)	2m 51s
Linting and tests / Helm Chart Unit Tests	15s
Linting and tests / Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: False)	3m 22s
Linting and tests / Unit tests - Migrators	19s
Snyk security scan / Snyk security scan	1m 40s
Linting and tests / Standard e2e tests / Grafana: 10.1.7	6m 31s
	36m 42s

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