Core/Spell: allow use of ground mounts while swimming (#17488)

src/server/game/Spells/Spell.cpp

@@ -5571,7 +5571,7 @@ SpellCastResult Spell::CheckCast(bool strict)
             }
             case SPELL_AURA_MOUNTED:
             {
-                if (m_caster->IsInWater())
+                if (m_caster->IsInWater() && m_spellInfo->HasAura(SPELL_AURA_MOD_INCREASE_MOUNTED_FLIGHT_SPEED))
                     return SPELL_FAILED_ONLY_ABOVEWATER;
 
                 // Ignore map check if spell have AreaId. AreaId already checked and this prevent special mount spells