fix linter errors

src/borg/archiver.py

@@ -1356,7 +1356,7 @@ class Archiver:
             tarinfo.uid = item.uid
             tarinfo.gid = item.gid
             tarinfo.uname = item.get('user', '')
-            tarinfo.gname = item.get('group',  '')
+            tarinfo.gname = item.get('group', '')
             # The linkname in tar has 2 uses:
             # for symlinks it means the destination, while for hardlinks it refers to the file.
             # Since hardlinks in tar have a different type code (LNKTYPE) the format might

src/borg/cache.py

@@ -1,5 +1,4 @@
 import configparser
-import json
 import os
 import shutil
 import stat
@@ -655,8 +654,6 @@ class LocalCache(CacheStatsMixin):
         archive indexes.
         """
         archive_path = os.path.join(self.path, 'chunks.archive.d')
-        # An index of chunks whose size had to be fetched
-        chunks_fetched_size_index = ChunkIndex()
         # Instrumentation
         processed_item_metadata_bytes = 0
         processed_item_metadata_chunks = 0