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

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

cscore/src/main/native/cpp/MjpegServerImpl.cpp

@@ -75,7 +75,7 @@ class MjpegServerImpl::ConnThread : public wpi::SafeThread {
   explicit ConnThread(const wpi::Twine& name, wpi::Logger& logger)
       : m_name(name.str()), m_logger(logger) {}
 
-  void Main();
+  void Main() override;
 
   bool ProcessCommand(wpi::raw_ostream& os, SourceImpl& source,
                       wpi::StringRef parameters, bool respond);

cscore/src/main/native/cpp/Notifier.cpp

@@ -68,7 +68,7 @@ class Notifier::Thread : public wpi::SafeThread {
   Thread(std::function<void()> on_start, std::function<void()> on_exit)
       : m_on_start(on_start), m_on_exit(on_exit) {}
 
-  void Main();
+  void Main() override;
 
   struct Listener {
     Listener() = default;

cscore/src/main/native/cpp/SinkImpl.h

@@ -29,7 +29,7 @@ class SinkImpl : public PropertyContainer {
  public:
   explicit SinkImpl(const wpi::Twine& name, wpi::Logger& logger,
                     Notifier& notifier, Telemetry& telemetry);
-  virtual ~SinkImpl();
+  ~SinkImpl() override;
   SinkImpl(const SinkImpl& queue) = delete;
   SinkImpl& operator=(const SinkImpl& queue) = delete;
 

cscore/src/main/native/cpp/SourceImpl.h

@@ -39,7 +39,7 @@ class SourceImpl : public PropertyContainer {
  public:
   SourceImpl(const wpi::Twine& name, wpi::Logger& logger, Notifier& notifier,
              Telemetry& telemetry);
-  virtual ~SourceImpl();
+  ~SourceImpl() override;
   SourceImpl(const SourceImpl& oth) = delete;
   SourceImpl& operator=(const SourceImpl& oth) = delete;
 

cscore/src/main/native/cpp/Telemetry.cpp

@@ -22,7 +22,7 @@ class Telemetry::Thread : public wpi::SafeThread {
  public:
   explicit Thread(Notifier& notifier) : m_notifier(notifier) {}
 
-  void Main();
+  void Main() override;
 
   Notifier& m_notifier;
   wpi::DenseMap<std::pair<CS_Handle, int>, int64_t> m_user;