Make schedule history migration idempotent

Author: durable-workflow-ops

src/migrations/2026_04_16_000180_create_workflow_schedule_history_events_table.php

@@ -27,6 +27,10 @@
 
     public function up(): void
     {
+        if (Schema::hasTable(self::TABLE)) {
+            return;
+        }
+
         Schema::create(self::TABLE, static function (Blueprint $table): void {
             $table->string('id', 26)
                 ->primary();