Issue #25030: Do not document seek() as if it accepts keyword arguments

Patch from Shiyao Ma.
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index 6498320..f643e91 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -490,7 +490,7 @@
 }
 
 PyDoc_STRVAR(seek_doc,
-"seek(pos, whence=0) -> int.  Change stream position.\n"
+"seek(pos[, whence]) -> int.  Change stream position.\n"
 "\n"
 "Seek to byte offset pos relative to position indicated by whence:\n"
 "     0  Start of stream (the default).  pos should be >= 0;\n"