build(deps): Bump connexion from 2.5.1 to 2.6.0 in /backend (#408)

Bumps [connexion](https://github.com/zalando/connexion) from 2.5.1 to 2.6.0.
- [Release notes](https://github.com/zalando/connexion/releases)
- [Commits](spec-first/connexion@2.5.1...2.6.0)

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==2.5.1
+connexion==2.6.0
 datadog==0.33.0
 fakeredis==1.1.0
 Flask==1.1.1