build(deps-dev): Bump pytest from 5.1.1 to 5.1.2 in /backend (#139)

Bump [pytest](https://github.com/pytest-dev/pytest) from 5.1.1 to 5.1.2.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@5.1.1...5.1.2)

Author: dependabot-preview[bot]

backend/requirements-dev.txt

@@ -1,4 +1,4 @@
 fakeredis==1.0.4
 pre-commit==1.18.3
-pytest==5.1.1
+pytest==5.1.2
 responses==0.10.6