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

@@ -10,7 +10,7 @@ drf-writable-nested==0.7.0
 django-oauth-toolkit==2.3.0
 django-debug-toolbar==4.2.0
 bleach==6.0.0
-gunicorn==20.1.0
+gunicorn==21.2.0
 lxml==5.1.0
 Markdown==3.5.1
 Pillow==10.2.0