TST: Fix case where there is no existing risk answer key.

The download checksum was not being correctly set when no file existed.
Set the checksum to the latest value so that a download is triggered.

tests/risk/answer_key.py

@@ -93,6 +93,8 @@ def ensure_latest_answer_key():
             else:
                 # Assume local copy that is being developed on
                 answer_key_dl_checksum = None
+    else:
+        answer_key_dl_checksum = ANSWER_KEY_CHECKSUMS[-1]
 
     if answer_key_dl_checksum:
         res = requests.get(