patch 8.2.2778: problem restoring 'packpath' in session

Problem:    Problem restoring 'packpath' in session.
Solution:   Let "skiprtp" also apply to 'packpath'.
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 80bb235..1f4c7e7 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -6511,7 +6511,7 @@
 			global values for local options)
 	   options	all options and mappings (also global values for local
 			options)
-	   skiprtp	exclude 'runtimepath' from the options
+	   skiprtp	exclude 'runtimepath' and 'packpath' from the options
 	   resize	size of the Vim window: 'lines' and 'columns'
 	   sesdir	the directory in which the session file is located
 			will become the current directory (useful with