build(deps): Bump zstandard from 0.12.0 to 0.13.0 in /backend (#348)

Bumps [zstandard](https://github.com/indygreg/python-zstandard) from 0.12.0 to 0.13.0.
- [Release notes](https://github.com/indygreg/python-zstandard/releases)
- [Changelog](https://github.com/indygreg/python-zstandard/blob/master/NEWS.rst)
- [Commits](indygreg/python-zstandard@0.12.0...0.13.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

backend/requirements.txt

@@ -11,4 +11,4 @@ python-dateutil==2.8.1
 pytoml==0.1.21
 redis==3.3.11
 swagger-ui-bundle==0.0.6
-zstandard==0.12.0
+zstandard==0.13.0