Update gunicorn requirement from <20.2,>=20.0 to >=20.0,<21.3

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@20.0.0...21.2.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
...

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

pyproject.toml

@@ -40,7 +40,7 @@ online = [
     "flask-cors>=3.0,<3.1",
     "panoptes-client>=1.6,<1.7",
     "requests>=2.28,<2.32",
-    "gunicorn>=20.0,<20.2",
+    "gunicorn>=20.0,<21.3",
     "sentry-sdk[flask]>=1.0,<1.30",
     "newrelic>=8.4.0,<9.1.2",
     "gitpython>=3.0.0,<3.2"