fix(DB): remove immunity to bleed effects on Boss (#9711)

Creatures affected:
- Ragnaros
- Baron Geddon
- Garr

data/sql/updates/pending_db_world/rev_1639521847268743300.sql

@@ -0,0 +1,3 @@
+INSERT INTO `version_db_world` (`sql_rev`) VALUES ('1639521847268743300');
+
+UPDATE `creature_template` SET `mechanic_immune_mask`= `mechanic_immune_mask`&~ 16384 WHERE (`entry` IN (11502, 12057, 12056));