test: replace localhost IP with 'localhost' for TLS conformity

test-https-connect-localport currently causes a runtime deprecation
warning: "[DEP0123] DeprecationWarning: Setting the TLS ServerName
to an IP address is not permitted by RFC 6066. This will be ignored
in a future version."

Change IP usage to the string 'localhost' instead.

PR-URL: #26881
Fixes: #26862
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>

Author: Trott

test/sequential/test-https-connect-localport.js

@@ -15,10 +15,10 @@ const assert = require('assert');
   }, common.mustCall(function(req, res) {
     this.close();
     res.end();
-  })).listen(0, common.localhostIPv4, common.mustCall(function() {
+  })).listen(0, 'localhost', common.mustCall(function() {
     const port = this.address().port;
     const req = https.get({
-      host: common.localhostIPv4,
+      host: 'localhost',
       pathname: '/',
       port,
       family: 4,