build(deps-dev): Bump responses from 0.10.7 to 0.10.8 in /backend (#326)

Bumps [responses](https://github.com/getsentry/responses) from 0.10.7 to 0.10.8.
- [Release notes](https://github.com/getsentry/responses/releases)
- [Changelog](https://github.com/getsentry/responses/blob/master/CHANGES)
- [Commits](getsentry/responses@0.10.7...0.10.8)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

backend/requirements-dev.txt

@@ -2,4 +2,4 @@ fakeredis==1.1.0
 pre-commit==1.20.0
 pytest==5.3.1
 pytest-responses==0.4.0
-responses==0.10.7
+responses==0.10.8