Bump ex_machina from 2.7.0 to 2.8.0 (#1136)

Bumps [ex_machina](https://github.com/beam-community/ex_machina) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/beam-community/ex_machina/releases)
- [Changelog](https://github.com/beam-community/ex_machina/blob/main/CHANGELOG.md)
- [Commits](beam-community/ex_machina@v2.7.0...v2.8.0)

---
updated-dependencies:
- dependency-name: ex_machina
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Add debug logs for staging

Fix DB crash due to timeout (#1031)

* Create index on assessment ID in submissions table

Improves read performance.

* Create separate view layer for grading summary

* Move views under AdminGradingView

* Migrate to more optimised query

* Use subquery instead of join for answers
* Split main model query and view model generation
* Split queries into 3
* Use ORM where possible

* Fix typing

* Restore group filtering functionality

* Update Avenger backlog notification workers

Fixes compatibilty with new function signature.

* Remove old query

* Remove comment

Bump Elixir and Erlang versions (#946)

* Reformat README

* Update GitHub workflow Elixir and OTP versions

* Update README versions

Contest leaderboard hiding (#826)

* Add contest leaderboard hiding

* fix open leaderboard wrong condition

Contest leaderboard hiding (#826)

* Add contest leaderboard hiding

* fix open leaderboard wrong condition

Add multitenant-stg-deploy to cd.yml

Merge branch 'dev/multitenent' of https://github.com/source-academy/c…

…adet into dev/multitenent