Make git.objects.util module docstring more specific

So git.objects.util is less likely to be confused with git.util.

(The modattrs.py script reveals the change in the value of
git.objects.util.__doc__, as expected.)

Author: EliahKagan

git/objects/util.py

@@ -3,7 +3,7 @@
 # This module is part of GitPython and is released under the
 # 3-Clause BSD License: https://opensource.org/license/bsd-3-clause/
 
-"""General utility functions."""
+"""General utility functions for working with git objects."""
 
 __all__ = (
     "get_object_type_by_name",