Update gunicorn requirement from <21.0,>=20.0 to >=21.2,<22.0 (#205)

Updates the requirements on [gunicorn](https://github.com/benoitc/gunicorn) to permit the latest version.
- [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
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 django>=4.2,<5.0
-gunicorn>=20.0,<21.0
+gunicorn>=21.2,<22.0
 dj-database-url>=2.0,<3.0
 whitenoise[brotli]>=6.0,<7.0