Add changelog entry for #32446

In #32446 was added method `dig` to `session`.
Improve docs of method `dig`.

[ci skip]

actionpack/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Add method `dig` to `session`.
+
+    *claudiob*, *Takumi Shotoku*
+
 *   Controller level `force_ssl` has been deprecated in favor of
     `config.force_ssl`.
 

actionpack/lib/action_dispatch/request/session.rb

@@ -93,8 +93,8 @@ def [](key)
         @delegate[key.to_s]
       end
 
-      # Returns the nested value specified by the sequence of key, returning
-      # nil if any intermediate step is nil.
+      # Returns the nested value specified by the sequence of keys, returning
+      # +nil+ if any intermediate step is +nil+.
       def dig(*keys)
         load_for_read!
         keys = keys.map.with_index { |key, i| i.zero? ? key.to_s : key }