Fix: Allowing only top-level organizations under participating organizations

coscine/issues#2355

src/Migrations/Migrations/Migration202302271200TopLevelProjectOrganizations.cs

+using FluentMigrator;
+
+namespace Coscine.Migrations.Migrations
+{
+    //yyyymmddhhmm
+    [Migration(202302271200)]
+    public class Migration202302271200TopLevelProjectOrganizations : Migration
+    {
+        public override void Up()
+        {
+            Execute.EmbeddedScript("Migration202302271200TopLevelProjectOrganizations_up.sql");
+        }
+        public override void Down()
+        {
+            // I've added no down script since the change itself has no correct reversal.
+        }
+    }
+}
\ No newline at end of file