CI: cleanup build warnings

Tests: fixed "unused const variable" warning
CMakeLists.txt: fixed deprecation warnings

src/tcp_server.cpp

@@ -573,13 +573,18 @@ bool TCPServer::send_internal(Client* client, Callback<size_t, uint8_t*, size_t>
 	return true;
 }
 
+const char* TCPServer::get_log_category() const
+{
+	return log_category_prefix;
+}
+
 void TCPServer::loop(void* data)
 {
 	TCPServer* server = static_cast<TCPServer*>(data);
 	server->m_loopThreadRunning.exchange(true);
 	ON_SCOPE_LEAVE([server]() { server->m_loopThreadRunning.exchange(false); });
 
-	log_category_prefix = server->get_category();
+	log_category_prefix = server->get_log_category();
 
 	LOGINFO(1, "event loop started");
 	server_event_loop_thread = data;