Fix test resource leak: dispose replication connection with await using

Agent-Logs-Url: https://github.com/npgsql/npgsql/sessions/2cf5ecb4-b7ee-446f-9ff1-b083c127e961 Co-authored-by: roji <1862641+roji@users.noreply.github.com>
Copilot · Apr 4, 2026 · Apr 4, 2026 · Apr 4, 2026 · Apr 4, 2026 · d590723b7c2d8a162bcdd5ea20e689c3eacdb9cf
commit d590723b7c2d8a162bcdd5ea20e689c3eacdb9cf
@@ -55,10 +55,10 @@ public void Open_on_disposed_connection()
             .EqualTo(typeof(TConnection).Name));
 
     [Test]
-    public void ConnectionString_cannot_be_set_when_created_with_data_source()
+    public async Task ConnectionString_cannot_be_set_when_created_with_data_source()
     {
-        using var dataSource = NpgsqlDataSource.Create(ConnectionString);
-        var rc = (TConnection)Activator.CreateInstance(typeof(TConnection), dataSource)!;
+        await using var dataSource = NpgsqlDataSource.Create(ConnectionString);
+        await using var rc = (TConnection)Activator.CreateInstance(typeof(TConnection), dataSource)!;
         Assert.Throws<InvalidOperationException>(() => rc.ConnectionString = "Host=localhost");
     }