hashers: convert salt to bytes before concatenation (#33226)

src/authentic2/hashers.py

@@ -80,7 +80,7 @@ class Drupal7PasswordHasher(hashers.BasePasswordHasher):
     def encode(self, password, salt, iterations):
         assert password
         assert salt and '$' not in salt
-        h = salt
+        h = force_bytes(salt)
         password = force_bytes(password)
         for i in range(iterations + 1):
             h = self.digest(h + password).digest()