build(deps-dev): bump responses from 0.11.0 to 0.12.0 in /backend

Bumps [responses](https://github.com/getsentry/responses) from 0.11.0 to 0.12.0.
- [Release notes](https://github.com/getsentry/responses/releases)
- [Changelog](https://github.com/getsentry/responses/blob/master/CHANGES)
- [Commits](getsentry/responses@0.11.0...0.12.0)

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

Author: dependabot[bot]

backend/requirements-dev.txt

@@ -2,4 +2,4 @@ fakeredis==1.4.3
 pre-commit==2.7.1
 pytest==6.0.1
 pytest-responses==0.4.0
-responses==0.11.0
+responses==0.12.0