Core/Players: Don't update mount capability while loading from db - auras are loaded before all known spell sources are processed

Closes #29391

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

@@ -7925,6 +7925,9 @@ MountCapabilityEntry const* Unit::GetMountCapability(uint32 mountType) const
 
 void Unit::UpdateMountCapability()
 {
+    if (IsLoading())
+        return;
+
     AuraEffectVector mounts = CopyAuraEffectList(GetAuraEffectsByType(SPELL_AURA_MOUNTED));
     for (AuraEffect* aurEff : mounts)
     {