Add missing migration with unique index

It was not "imported" from the extended model, so basically it was ignored..

Author: LucaGallinari

src/Migrations/Version20260227151801.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Webgriffe\SyliusActiveCampaignPlugin\Migrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20260227151801 extends AbstractMigration
+{
+    public function up(Schema $schema): void
+    {
+        $this->addSql('CREATE UNIQUE INDEX channel_customer_idx ON webgriffe_sylius_active_campaign_channel_customer (channel_id, customer_id)');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->addSql('DROP INDEX channel_customer_idx ON webgriffe_sylius_active_campaign_channel_customer');
+    }
+}

tests/TestApplication/src/Entity/Customer/ChannelCustomer.php

@@ -9,6 +9,7 @@
 
 #[ORM\Entity]
 #[ORM\Table(name: 'webgriffe_sylius_active_campaign_channel_customer')]
+#[ORM\UniqueConstraint(name: 'channel_customer_idx', columns: ['channel_id', 'customer_id'])]
 class ChannelCustomer extends BaseChannelCustomer
 {
 }