Bump database_cleaner from 2.0.2 to 2.1.0 in /backend

Bumps [database_cleaner](https://github.com/DatabaseCleaner/database_cleaner) from 2.0.2 to 2.1.0.
- [Changelog](https://github.com/DatabaseCleaner/database_cleaner/blob/main/History.rdoc)
- [Commits](DatabaseCleaner/database_cleaner@v2.0.2...v2.1.0)

---
updated-dependencies:
- dependency-name: database_cleaner
  dependency-version: 2.1.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/Gemfile.lock

@@ -143,11 +143,11 @@ GEM
     cuprite (0.15)
       capybara (~> 3.0)
       ferrum (~> 0.14.0)
-    database_cleaner (2.0.2)
+    database_cleaner (2.1.0)
       database_cleaner-active_record (>= 2, < 3)
-    database_cleaner-active_record (2.1.0)
+    database_cleaner-active_record (2.2.2)
       activerecord (>= 5.a)
-      database_cleaner-core (~> 2.0.0)
+      database_cleaner-core (~> 2.0)
     database_cleaner-core (2.0.1)
     database_cleaner-mongoid (2.0.1)
       database_cleaner-core (~> 2.0.0)