Bump the dependencies group with 1 update (#611)

Bumps the dependencies group with 1 update: [service-identity](https://github.com/pyca/service-identity).

- [Release notes](https://github.com/pyca/service-identity/releases)
- [Changelog](https://github.com/pyca/service-identity/blob/main/CHANGELOG.md)
- [Commits](pyca/service-identity@21.1.0...23.1.0)

---
updated-dependencies:
- dependency-name: service-identity
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: dependencies
...

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

test-requirements.txt

@@ -35,7 +35,5 @@ pyopenssl==23.2.0
     # via -r test-requirements.in
 pytest==7.4.0
     # via -r test-requirements.in
-service-identity==21.1.0
+service-identity==23.1.0
     # via -r test-requirements.in
-six==1.16.0
-    # via service-identity