[3.12] gh-125818: Fix incorrect signature of argument skip_file_prefixes in warnings docs (GH-125823) (GH-126217)

gh-125818: Fix incorrect signature of argument `skip_file_prefixes` in warnings docs (GH-125823)

Change documentation
(cherry picked from commit d467d92)

Co-authored-by: RUANG (James Roy) <[email protected]>

Author: miss-islington

Doc/library/warnings.rst

@@ -396,7 +396,7 @@ Available Functions
 -------------------
 
 
-.. function:: warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=None)
+.. function:: warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=())
 
    Issue a warning, or maybe ignore it or raise an exception.  The *category*
    argument, if given, must be a :ref:`warning category class <warning-categories>`; it