TRoW::13: fixed a bug found by myself in the Sea Serpent event.

changelog

@@ -9,6 +9,8 @@ Version 1.9.14+svn:
        the original unit selected at the start of the scenario died
    * Under the Burning Suns:
      * Scenario 5: Fixed bug #19303: one of the dwarves was spawning in a wall.
+   * The Rise of Wesnoth:
+     * Peoples in Decline: fixed a message not shown when the Sea Serpent appears
  * Editor:
    * Added Etheral Abyss terrain (Qxua) to the Cave category, too
    * Updated the terrain palette icons for winter/fall single or mixed forested

data/campaigns/The_Rise_Of_Wesnoth/scenarios/13_Peoples_in_Decline.cfg

@@ -242,7 +242,11 @@
             # wmllint: recognize Bitey The Sepent
 
             [message]
-                speaker=unit
+                side=1
+                [filter_location]
+                    x,y=$xx1,$yy1
+                    radius=10
+                [/filter_location]
                 message= _ "Look out, a serpent has emerged from the deep."
             [/message]