test: make test-tls-invoke-queued use public API

`parallel/test-tls-invoke-queued` previously used the internal
`_write()` API to hook into the internals more directly, but this
invalidates the general assumption made by streams APIs that
only a single write is active at a time, and which is enforced
through the public API.

PR-URL: #17864
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-tls-invoke-queued.js

@@ -36,12 +36,12 @@ const server = tls.createServer({
   key: fixtures.readKey('agent1-key.pem'),
   cert: fixtures.readKey('agent1-cert.pem')
 }, common.mustCall(function(c) {
-  c._write('hello ', null, common.mustCall(function() {
-    c._write('world!', null, common.mustCall(function() {
+  c.write('hello ', null, common.mustCall(function() {
+    c.write('world!', null, common.mustCall(function() {
       c.destroy();
     }));
     // Data on next _write() will be written but callback will not be invoked
-    c._write(' gosh', null, common.mustNotCall());
+    c.write(' gosh', null, common.mustNotCall());
   }));
 
   server.close();