build(deps-dev): Bump pre-commit from 2.5.1 to 2.6.0 in /backend

Bumps [pre-commit](https://github.com/pre-commit/pre-commit) from 2.5.1 to 2.6.0.
- [Release notes](https://github.com/pre-commit/pre-commit/releases)
- [Changelog](https://github.com/pre-commit/pre-commit/blob/master/CHANGELOG.md)
- [Commits](pre-commit/pre-commit@v2.5.1...v2.6.0)

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

Author: dependabot-preview[bot]

backend/requirements-dev.txt

@@ -1,5 +1,5 @@
 fakeredis==1.4.1
-pre-commit==2.5.1
+pre-commit==2.6.0
 pytest==5.4.3
 pytest-responses==0.4.0
 responses==0.10.15