Update gunicorn requirement from >=23.0.0 to >=26.1.0

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@23.0.0...26.1.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-version: 26.1.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -206,5 +206,5 @@ cryptography>=50.0.0
 # CI asserts the installed version inside the built image — a transitive pin
 # (markdown2dash asks for gunicorn<22) must never be allowed to drag the
 # production server back under the floor without failing the build.
-gunicorn>=23.0.0
+gunicorn>=26.1.0
 # uvicorn[standard]>=0.27.0