Core/Misc: don't allow players to use/activate/loot non-allowed gameobjects while under the effect of a damage immunity aura (#23319)

* Core/Misc: don't allow players to use/activate/loot non-allowed gameobjects while under the effect of a damage immunity aura.

* Forgot to change this in last-second rename.

* Apply suggested changes, thanks Shauren!

# Conflicts:
#	src/server/game/Entities/GameObject/GameObject.cpp
#	src/server/game/Entities/Unit/UnitDefines.h
#	src/server/game/Entities/Unit/enuminfo_UnitDefines.cpp
#	src/server/scripts/Outland/CoilfangReservoir/TheSlavePens/boss_ahune.cpp

src/server/game/Entities/Unit/UnitDefines.h

@@ -151,7 +151,7 @@ enum UnitFlags : uint32
     UNIT_FLAG_UNK_28                = 0x10000000,
     UNIT_FLAG_UNK_29                = 0x20000000,           // used in Feing Death spell
     UNIT_FLAG_SHEATHE               = 0x40000000,
-    UNIT_FLAG_UNK_31                = 0x80000000,
+    UNIT_FLAG_IMMUNE                = 0x80000000,           // Immune to damage
     MAX_UNIT_FLAGS = 33
 };