fix(Scripts/Midsummer): Add SpellScript for "Fire Festival Fortitude" (#18246)

- implement zone wide buff
- Blizzard originally used gameobject 181431 'Fire Festival Fury Trap'
  for this implementation

data/sql/updates/pending_db_world/rev_1706729918749943200.sql

@@ -0,0 +1,4 @@
+-- Midsummer - add spell script for 29235 Fire Festival Fortitude
+DELETE FROM `spell_script_names` WHERE `spell_id` = 29235;
+INSERT INTO `spell_script_names` (`spell_id`, `ScriptName`) VALUES
+(29235, 'spell_fire_festival_fortitude');