Bump gunicorn from 20.1.0 to 21.2.0

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 20.1.0 to 21.2.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@20.1.0...21.2.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -51,5 +51,5 @@ pytest==7.4.0
 # Indirect, but required dependencies (often required for efficient deployments)
 gevent==22.10.2
 greenlet==2.0.2
-gunicorn==20.1.0
+gunicorn==21.2.0
 importlib-metadata==6.8.0 # See https://github.com/hotosm/tasking-manager/issues/5395