Bump gunicorn from 22.0.0 to 23.0.0 in /tests/test_gcloud/testbench (#2138)

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 22.0.0 to 23.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@22.0.0...23.0.0)

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

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Author: dependabot[bot]

tests/test_gcloud/testbench/requirements.txt

@@ -2,4 +2,4 @@ crc32c==2.1
 flask==2.3.2
 greenlet==0.4.17
 gevent==23.9.1
-gunicorn==22.0.0
+gunicorn==23.0.0