Value is unused, indicate that by leading underscore (flake8)

in fix_journal we reset the value of a password prop discardig the old value.

Author: rouilj

roundup/backends/back_anydbm.py

@@ -571,7 +571,7 @@ def fix_journal(self, classname, journal):
             return journal
         for j in journal:
             if j[3] == 'set':
-                for k, v in j[4].items():
+                for k, _v in j[4].items():
                     if k in pwprops and j[4][k]:
                         j[4][k] = password.JournalPassword(j[4][k])
         return journal