test: replace flag with option

test-https-agent-additional-options is invoked with a command-line flag.
However, there is an equivalent option that can be enabled within the
code. Do that instead.

PR-URL: #27830
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-https-agent-additional-options.js

@@ -1,4 +1,3 @@
-// Flags: --tls-min-v1.1
 'use strict';
 const common = require('../common');
 if (!common.hasCrypto)
@@ -12,7 +11,8 @@ const fixtures = require('../common/fixtures');
 const options = {
   key: fixtures.readKey('agent1-key.pem'),
   cert: fixtures.readKey('agent1-cert.pem'),
-  ca: fixtures.readKey('ca1-cert.pem')
+  ca: fixtures.readKey('ca1-cert.pem'),
+  minVersion: 'TLSv1.1',
 };
 
 const server = https.Server(options, function(req, res) {