Bump persistent from 5.2 to 6.0

Bumps [persistent](https://github.com/zopefoundation/persistent) from 5.2 to 6.0.
- [Changelog](https://github.com/zopefoundation/persistent/blob/master/CHANGES.rst)
- [Commits](zopefoundation/persistent@5.2...6.0)

---
updated-dependencies:
- dependency-name: persistent
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -2,7 +2,7 @@ BTrees==5.2
 cffi==1.16.0
 dnspython==2.6.1
 mysql-connector==2.2.9
-persistent==5.2
+persistent==6.0
 pycparser==2.22
 pymongo==4.7.2
 six==1.16.0