Bump gevent from 20.9.0 to 23.9.1 in /tests/test_gcloud/testbench (#1864

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Bumps [gevent](https://github.com/gevent/gevent) from 20.9.0 to 23.9.1.
- [Release notes](https://github.com/gevent/gevent/releases)
- [Changelog](https://github.com/gevent/gevent/blob/master/docs/changelog_pre.rst)
- [Commits](gevent/gevent@20.9.0...23.9.1)

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

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

tests/test_gcloud/testbench/requirements.txt

@@ -1,5 +1,5 @@
 crc32c==2.1
 flask==2.3.2
 greenlet==0.4.17
-gevent==20.9.0
+gevent==23.9.1
 gunicorn==20.0.4