fix(deps): bump gunicorn from 20.1.0 to 21.2.0 (#98)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -28,4 +28,4 @@ sqlalchemy      == 2.0.25
 flask-sqlalchemy >= 3.0.1
 psycopg2        == 2.9.9
 flask-migrate   == 3.1.0
-gunicorn        == 20.1.0
+gunicorn        == 21.2.0