Mock the substack domain also when testing redirects

We were making the actual call to the redirected URL here,
instead of mocking it. We need to mock both the embedded email
domain, and the domain we are redirected to.

packages/content-handler/test/newsletter.test.ts

@@ -172,8 +172,9 @@ describe('Newsletter email test', () => {
             Location:
               'https://newsletter.slowchinese.net/p/companies-that-eat-people-217',
           })
-          .get('/p/companies-that-eat-people-217')
-          .reply(200, '')
+          nock('https://newsletter.slowchinese.net')
+            .head('/p/companies-that-eat-people-217')
+            .reply(200, '')
       })
       after(() => {
         nock.restore()
@@ -186,7 +187,7 @@ describe('Newsletter email test', () => {
         expect(url).to.startWith(
           'https://newsletter.slowchinese.net/p/companies-that-eat-people-217'
         )
-      }).timeout(10000)
+      })
     })
 
     context('when email is from beehiiv', () => {