build(deps-dev): bump fakeredis from 2.19.0 to 2.20.0 in /backend (#2132)

Bumps [fakeredis](https://github.com/cunla/fakeredis-py) from 2.19.0 to 2.20.0.
- [Release notes](https://github.com/cunla/fakeredis-py/releases)
- [Commits](cunla/fakeredis-py@v2.19.0...v2.20.0)

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

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -1,4 +1,4 @@
-fakeredis==2.19.0
+fakeredis==2.20.0
 pre-commit==3.5.0
 pytest==7.4.3
 pytest-responses==0.5.1