lib: fix Host header when CONNECT ProxyAgent

Author: RafaelGSS

lib/proxy-agent.js

@@ -97,7 +97,7 @@ class ProxyAgent extends DispatcherBase {
             signal: opts.signal,
             headers: {
               ...this[kProxyHeaders],
-              host
+              host: requestedHost,
             }
           })
           if (statusCode !== 200) {

test/proxy-agent.js

@@ -393,7 +393,7 @@ test('ProxyAgent correctly sends headers when using fetch - #1355, #1623', async
   }
 
   const expectedProxyHeaders = {
-    host: `localhost:${proxy.address().port}`,
+    host: `localhost:${server.address().port}`,
     connection: 'close'
   }