Update factory function for creating sample Dandiset for tests

This update is for meeting the requirement of having
email for a contributor who is a contact person
imposed by dandischema,
dandi/dandi-schema#235

dandi/tests/fixtures.py

@@ -548,6 +548,7 @@ def mkdandiset(self, name: str, embargo: bool = False) -> SampleDandiset:
                     {
                         "schemaKey": "Person",
                         "name": "Tests, Dandi-Cli",
+                        "email": "nemo@example.com",
                         "roleName": ["dcite:Author", "dcite:ContactPerson"],
                     }
                 ],