Bump gunicorn from 20.1.0 to 21.2.0 in /src (#3470)

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
...

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

Author: dependabot[bot]

src/requirements.txt

@@ -1,6 +1,6 @@
 flask==2.3.2
 flask-talisman==1.0.0
-gunicorn==20.1.0
+gunicorn==21.2.0
 pytest==7.4.0
 pytest-watch==4.2.0
 pytest-cov==4.1.0