The connection reserved for LISTEN is not closed after the last subscribed-to channel is unsubscribed from

I noticed that the Node.js process does not come to an end after using the listening mechanism. That's because the connection reserved for LISTEN statements is not closed even after the last channel is unsubscribed from. And even if all other connections are closed via close().

Use this program:

const sql = require("postgres")(...);

sql.listen("topic", console.log.bind(null, "Received:"), async () => {
	await sql.unsafe(`SELECT pg_notify('topic', 'something')`);
}).then(({ unlisten }) => {
	setTimeout(async () => {
		await sql.close();
		await unlisten();
		// sql.unsafe(`SELECT 1`);
	}, 1000);
});

Start by running the JavaScript reproduction in the issue and inspect the listen/unlisten connection lifecycle. The fix is complete when closing the client and unsubscribing from the last channel allow the Node.js process to exit without another query keeping the connection open.