preprocess_args: fix option name matching

previously, it also matched on --sort-by when it only should have matched on --sort.

Author: ThomasWaldmann

src/borg/archiver/__init__.py

@@ -180,7 +180,8 @@ def preprocess_args(self, args):
         ]
         for i, arg in enumerate(args[:]):
             for old_name, new_name, warning in deprecations:
-                if arg.startswith(old_name):
+                # either --old_name or --old_name=...
+                if arg == old_name or (arg.startswith(old_name) and arg[len(old_name)] == "="):
                     if new_name is not None:
                         args[i] = arg.replace(old_name, new_name)
                     print(warning, file=sys.stderr)