# What this PR does
- `AlertGroupPostMortem` has no references in the codebase.. I stumbled
across it while working on https://github.com/grafana/oncall/pull/5224
and decided to just remove it
- Removing old Slack channel related `VARCHAR` columns; these were
refactored to foreign key references to `slack_slackchannel` table in
following PRs:
- https://github.com/grafana/oncall/pull/5224
- https://github.com/grafana/oncall/pull/5199
- https://github.com/grafana/oncall/pull/5191
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
show up in the autogenerated release notes.
# What this PR does
This PR adds
[django-migration-linter](https://github.com/3YOURMIND/django-migration-linter)
to keep database migrations
backwards compatible
- we can automatically run migrations and they are zero-downtime, e.g.
old code can work with the migrated database
- we can run and rollback migrations without worrying about data safety
- OnCall is deployed to the multiple environments core team is not able
to control
See [django-migration-linter
checklist](https://github.com/3YOURMIND/django-migration-linter/blob/main/docs/incompatibilities.md)
for the common mistakes and best practices
## Which issue(s) this PR fixes
## Checklist
- [ ] Tests updated
- [ ] Documentation added
- [ ] `CHANGELOG.md` updated
---------
Co-authored-by: Joey Orlando <joey.orlando@grafana.com>
