use proper global variable to check if shared custody should be used

src/Utils/TAVCotisationUtils.php

@@ -215,7 +215,7 @@ class TAVCotisationUtils
 
         // increment allowance for each dependant child, depending on the shared custody arrangement
         $useSharedCustody = $this->em->getRepository(GlobalParameter::class)
-            ->val(GlobalParameter::SSA_HOUSEHOLD_SECONDARY_AMOUNT);
+            ->val(GlobalParameter::SSA_HOUSEHOLD_USE_SHARED_CUSTODY);
         $childUnderLimitAmount = (int) $this->em->getRepository(GlobalParameter::class)
             ->val(GlobalParameter::SSA_HOUSEHOLD_DEPENDANT_CHILD_UNDER_LIMIT_AMOUNT);