Update max elements in ActionsBlock to 25

It seems from practical testing with the slack block kit builder that the (new?) max number of elements allowed in an ActionsBlock is 25, rather than 5 as previously shown in the code.

Update 5 -> 25 in docstring as well

Author: YSaxon

slack_sdk/models/blocks/blocks.py

@@ -257,7 +257,7 @@ def _validate_title_length(self):
 
 class ActionsBlock(Block):
     type = "actions"
-    elements_max_length = 5
+    elements_max_length = 25
 
     @property
     def attributes(self) -> Set[str]:
@@ -275,7 +275,7 @@ def __init__(
 
         Args:
             elements (required): An array of interactive element objects - buttons, select menus, overflow menus,
-                or date pickers. There is a maximum of 5 elements in each action block.
+                or date pickers. There is a maximum of 25 elements in each action block.
             block_id: A string acting as a unique identifier for a block.
                 If not specified, a block_id will be generated.
                 You can use this block_id when you receive an interaction payload to identify the source of the action.