fix: make POSIX event thread safe

Foundation/include/Poco/Event_POSIX.h

@@ -39,8 +39,8 @@ protected:
 	void resetImpl();
 
 private:
-	bool            _auto;
-	bool            _state;
+	std::atomic<bool> _auto;
+	std::atomic<bool> _state;
 	pthread_mutex_t _mutex;
 	pthread_cond_t  _cond;
 };