Core/Spells: do not apply unit_state_casting for instant cast spells.

src/server/game/Entities/Unit/Unit.cpp

@@ -2893,6 +2893,7 @@ void Unit::SetCurrentCastedSpell(Spell* pSpell)
                     InterruptSpell(CURRENT_AUTOREPEAT_SPELL);
                 m_AutoRepeatFirstCast = true;
             }
+            if (m_currentSpells[CURRENT_GENERIC_SPELL]->m_spellInfo->CalcCastTime(this) > 0 && IsNonMeleeSpellCasted(false, false, true))
                 AddUnitState(UNIT_STATE_CASTING);
         } break;