Update zope-testrunner requirement from <6,>=5 to >=5,<7

Updates the requirements on [zope-testrunner](https://github.com/zopefoundation/zope.testrunner) to permit the latest version.
- [Release notes](https://github.com/zopefoundation/zope.testrunner/releases)
- [Changelog](https://github.com/zopefoundation/zope.testrunner/blob/master/CHANGES.rst)
- [Commits](zopefoundation/zope.testrunner@5.0...6.0)

---
updated-dependencies:
- dependency-name: zope-testrunner
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

setup.py

@@ -65,7 +65,7 @@ def read(path):
                     'backports.zoneinfo<1; python_version<"3.9"'],
         test=['tox>=3,<5',
               'zope.testing>=4,<6',
-              'zope.testrunner>=5,<6',
+              'zope.testrunner>=5,<7',
               'zc.customdoctests>=1.0.1,<2',
               'createcoverage>=1,<2',
               'stopit>=1.1.2,<2',