Upgrade coverage to 6.5.0

We received error messages in older version of the coverage so we
upgrade to the version 6.5.0 which seems to work with the coveralls.

See this run for more details:
https://github.com/Parquery/icontract/actions/runs/9779072024/job/26997391256?pr=292

setup.py

@@ -57,7 +57,7 @@
             'pylint==2.17.5;python_version>="3.7"',
             "tox>=3.0.0",
             "pydocstyle>=6.3.0,<7",
-            "coverage>=4.5.1,<5",
+            "coverage>=6.5.0,<7",
             "docutils>=0.14,<1",
             "pygments>=2.2.0,<3",
             "dpcontracts==0.6.0",