build(deps): Bump connexion from 2.3.0 to 2.4.0 in /backend (#228)

Bumps [connexion](https://github.com/zalando/connexion) from 2.3.0 to 2.4.0.
- [Release notes](https://github.com/zalando/connexion/releases)
- [Commits](spec-first/connexion@2.3.0...2.4.0)

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

Author: dependabot-preview[bot]

backend/requirements.txt

@@ -1,5 +1,5 @@
 -e ../tools #egg=code-coverage-tools
-connexion==2.3.0
+connexion==2.4.0
 datadog==0.30.0
 Flask==1.1.1
 Flask-Cors==3.0.8