Bump mongo from 2.20.1 to 2.21.0

Bumps [mongo](https://github.com/mongodb/mongo-ruby-driver) from 2.20.1 to 2.21.0.
- [Release notes](https://github.com/mongodb/mongo-ruby-driver/releases)
- [Commits](mongodb/mongo-ruby-driver@v2.20.1...v2.21.0)

---
updated-dependencies:
- dependency-name: mongo
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -261,7 +261,7 @@ GEM
     mini_mime (1.1.5)
     mini_portile2 (2.8.7)
     minitest (5.25.1)
-    mongo (2.20.1)
+    mongo (2.21.0)
       bson (>= 4.14.1, < 6.0.0)
     mongoid (9.0.1)
       activemodel (>= 5.1, < 7.2, != 7.0.0)