Bump gevent from 21.1.0 to 21.1.1 in /backend

Bumps [gevent](https://github.com/gevent/gevent) from 21.1.0 to 21.1.1.
- [Release notes](https://github.com/gevent/gevent/releases)
- [Changelog](https://github.com/gevent/gevent/blob/master/docs/changelog_pre.rst)
- [Commits](gevent/gevent@21.1.0...21.1.1)

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

Author: dependabot-preview[bot]

backend/requirements.txt

@@ -1,5 +1,5 @@
 flask>=0.12.3
-gevent==21.1.0
+gevent==21.1.1
 Flask-Cors==3.0.10
 Flask-Security==3.0.0
 Flask-SQLAlchemy==2.4.3