Bump gunicorn from 20.0.4 to 23.0.0 in /app

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 20.0.4 to 23.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@20.0.4...23.0.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-version: 23.0.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

app/requirements.txt

@@ -29,7 +29,7 @@ drf-haystack==1.8.10
 elasticsearch==7.8.1
 filelock==3.0.12
 gprof2dot==2019.11.30
-gunicorn==20.0.4
+gunicorn==23.0.0
 html5lib==1.1
 idna==2.10
 importlib-metadata==1.7.0