build(deps): bump fakeredis from 1.8.2 to 1.9.1 in /backend (#1557)

Bumps [fakeredis](https://github.com/cunla/fakeredis-py) from 1.8.2 to 1.9.1.
- [Release notes](https://github.com/cunla/fakeredis-py/releases)
- [Commits](cunla/fakeredis-py@v1.8.2...v1.9.1)

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

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -1,4 +1,4 @@
-fakeredis==1.8.2
+fakeredis==1.9.1
 pre-commit==2.20.0
 pytest==7.1.3
 pytest-responses==0.5.0

backend/requirements.txt

@@ -1,7 +1,7 @@
 -e ../tools #egg=code-coverage-tools
 connexion==2.14.0
 datadog==0.44.0
-fakeredis==1.8.2
+fakeredis==1.9.1
 Flask==2.1.3
 Flask-Cors==3.0.10
 flask-talisman==1.0.0