Fixed test that left an instance of ghost running (#21178)

no issue

- This test file starts a Ghost server, but doesn't close it, which can
cause other tests to fail when they try to start an instance of Ghost,
with an `EADDRINUSE` error.
- This change closes the server in the `after` hook

ghost/core/test/e2e-server/click-tracking.test.js

@@ -8,11 +8,11 @@ const membersEventsService = require('../../core/server/services/members-events'
 
 describe('Click Tracking', function () {
     let agent;
+    let ghostServer;
     let webhookMockReceiver;
 
     before(async function () {
-        const {adminAgent} = await agentProvider.getAgentsWithFrontend();
-        agent = adminAgent;
+        ({adminAgent: agent, ghostServer} = await agentProvider.getAgentsWithFrontend());
         await fixtureManager.init('newsletters', 'members:newsletters', 'integrations');
         await agent.loginAsOwner();
     });
@@ -28,6 +28,10 @@ describe('Click Tracking', function () {
         mockManager.restore();
     });
 
+    after(async function () {
+        await ghostServer.stop();
+    });
+
     it('Full test', async function () {
         const siteUrl = new URL(urlUtils.urlFor('home', true));