change default value from $index to a fixed 0.

Closes #3257438

src/Element/ConditionsTable.php

@@ -200,7 +200,7 @@ class ConditionsTable extends FormElement {
         '#type' => 'checkbox',
         '#title' => t('Negate'),
         '#parents' => array_merge($element['#parents'], [$index, 'negate_condition']),
-        '#default_value' => $condition['configuration']['negate_condition'] ?? $index,
+        '#default_value' => $condition['configuration']['negate_condition'] ?? 0,
         '#access' => !isset($condition_form['configuration']['form']['negate']),
       ];