Bump discord-webhook from 0.16.0 to 0.16.3 in /backend

Bumps [discord-webhook](https://github.com/lovvskillz/python-discord-webhook) from 0.16.0 to 0.16.3.
- [Release notes](https://github.com/lovvskillz/python-discord-webhook/releases)
- [Changelog](https://github.com/lovvskillz/python-discord-webhook/blob/master/CHANGES.md)
- [Commits](https://github.com/lovvskillz/python-discord-webhook/compare/0.16.0...0.16.3)

---
updated-dependencies:
- dependency-name: discord-webhook
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/requirements.txt

@@ -7,6 +7,6 @@ python-socketio==4.6.1
 six==1.16.0
 pytest==7.1.2
 requests==2.27.1
-discord-webhook==0.16.0
+discord-webhook==0.16.3
 datadog==0.44.0
 ddtrace==1.1.2