use mocks for isni API calls

- fixes a couple of tests making author ISNI calls
- notes a future TODO to remove some possibly useless code

bookwyrm/utils/isni.py

@@ -85,6 +85,8 @@ def find_authors_by_name(name_string, description=False):
     # build list of possible authors
     possible_authors = []
     for element in root.iter("responseRecord"):
+
+        # TODO: we don't seem to do anything with the personal_name variable - is this code block needed?
         personal_name = element.find(".//forename/..")
         if not personal_name:
             continue