adaptive: MovingAverage: fix template-id warning

In file included from ../../modules/demux/adaptive/logic/RateBasedAdaptationLogic.h:29,
                 from ../../modules/demux/adaptive/logic/RateBasedAdaptationLogic.cpp:28:
../../modules/demux/adaptive/logic/../tools/MovingAverage.hpp:32:33: warning: template-id not allowed for constructor in C++20 [-Wtemplate-id-cdtor]
   32 |             MovingAverageSum<T>(T i): sum(0), prev(i) { }
      |                                 ^
../../modules/demux/adaptive/logic/../tools/MovingAverage.hpp:32:33: note: remove the ‘< >’