clang-tidy: modernize-use-override (NFC)

Add NOLINT to CommandTestBase due to gmock not adding "override" keyword,
which causes warnings on clang.

ntcore/src/main/native/cpp/CallbackManager.h

@@ -54,7 +54,7 @@ class CallbackThread : public wpi::SafeThread {
   using NotifierData = TNotifierData;
   using ListenerData = TListenerData;
 
-  ~CallbackThread() {
+  ~CallbackThread() override {
     // Wake up any blocked pollers
     for (size_t i = 0; i < m_pollers.size(); ++i) {
       if (auto poller = m_pollers[i]) {

ntcore/src/main/native/cpp/Dispatcher.h

@@ -41,7 +41,7 @@ class DispatcherBase : public IDispatcher {
 
   DispatcherBase(IStorage& storage, IConnectionNotifier& notifier,
                  wpi::Logger& logger);
-  virtual ~DispatcherBase();
+  ~DispatcherBase() override;
 
   unsigned int GetNetworkMode() const;
   void StartLocal();

ntcore/src/main/native/cpp/DsClient.cpp

@@ -19,7 +19,7 @@ class DsClient::Thread : public wpi::SafeThread {
   Thread(Dispatcher& dispatcher, wpi::Logger& logger, unsigned int port)
       : m_dispatcher(dispatcher), m_logger(logger), m_port(port) {}
 
-  void Main();
+  void Main() override;
 
   Dispatcher& m_dispatcher;
   wpi::Logger& m_logger;

ntcore/src/main/native/cpp/NetworkConnection.h

@@ -49,7 +49,7 @@ class NetworkConnection : public INetworkConnection {
                     IConnectionNotifier& notifier, wpi::Logger& logger,
                     HandshakeFunc handshake,
                     Message::GetEntryTypeFunc get_entry_type);
-  ~NetworkConnection();
+  ~NetworkConnection() override;
 
   // Set the input processor function.  This must be called before Start().
   void set_process_incoming(ProcessIncomingFunc func) {

ntcore/src/main/native/cpp/Storage.h

@@ -47,7 +47,7 @@ class Storage : public IStorage {
   Storage(const Storage&) = delete;
   Storage& operator=(const Storage&) = delete;
 
-  ~Storage();
+  ~Storage() override;
 
   // Accessors required by Dispatcher.  An interface is used for
   // generation of outgoing messages to break a dependency loop between