SortBySpec: avoid triggering bandit security checker

Guess it was triggered due to naming the variable "token",
maybe "sort_key" is less problematic.

Author: ThomasWaldmann

src/borg/helpers/parseformat.py

@@ -351,9 +351,9 @@ def FilesystemPathSpec(text):
 def SortBySpec(text):
     from ..manifest import AI_HUMAN_SORT_KEYS
 
-    for token in text.split(","):
-        if token not in AI_HUMAN_SORT_KEYS and token != "ts":  # idempotency: do not reject ts
-            raise argparse.ArgumentTypeError("Invalid sort key: %s" % token)
+    for sort_key in text.split(","):
+        if sort_key not in AI_HUMAN_SORT_KEYS and sort_key != "ts":  # idempotency: do not reject ts
+            raise argparse.ArgumentTypeError("Invalid sort key: %s" % sort_key)
     return text.replace("timestamp", "ts").replace("archive", "name")