odb: pin index pickle protocol version

dvc/objects/db/index.py

@@ -88,7 +88,7 @@ class ObjectDBIndex(ObjectDBIndexBase):
         tmp_dir: "StrPath",
         name: str,
     ):  # pylint: disable=super-init-not-called
-        from diskcache import Index
+        from diskcache import Cache, Index
 
         from dvc.fs.local import LocalFileSystem
         from dvc.utils.fs import makedirs
@@ -96,7 +96,13 @@ class ObjectDBIndex(ObjectDBIndexBase):
         self.index_dir = os.path.join(tmp_dir, self.INDEX_DIR, name)
         makedirs(self.index_dir, exist_ok=True)
         self.fs = LocalFileSystem()
-        self.index = Index(self.index_dir)
+        self.index = Index.fromcache(
+            Cache(
+                self.index_dir,
+                disk_pickle_protocol=4,
+                eviction_policy="none",
+            )
+        )
 
     def __iter__(self):
         return iter(self.index)