MDEV-37031 Fix broken server_audit.test on Windows

- The test was inadvertently skipped on Windows CI, due to the
  unjustified addition of include/have_tlsv13.inc in MDEV-33834 (log TLS
  version). That include didn't make sense here and just reduced
  coverage.

- Once skipped, the test got broken later by MDEV-12182 changes.
  Originally it expected only one localhost:PORT line in the audit log,
  assuming Unix socket connections. But on Windows, MTR uses TCP by
  default, so all entries had :PORT, and the diff failed.

Fix:
- Forced tcp connection for server_audit.test, via .cnf file
  Re-recorded result
  unix_socket + server_audit is still covered by other tests.
- Dropped the have_tlsv13.inc include to restore coverage—it wasn't
  testing TLS versions or ciphers anyway

mysql-test/suite/plugins/t/server_audit.cnf

@@ -0,0 +1,4 @@
+!include include/default_my.cnf
+
+[mysqltest]
+protocol=tcp

mysql-test/suite/plugins/t/server_audit.test

@@ -1,7 +1,6 @@
 --source include/have_plugin_auth.inc
 --source include/not_embedded.inc
 --source include/have_ssl_communication.inc
---source include/have_tlsv13.inc
 
 if (!$SERVER_AUDIT_SO) {
   skip No SERVER_AUDIT plugin;