Delay emitting metadata porting warnings until KF 5.75
Otherwise everyone running KF >= 5.72 with Plasma 5.19 would get the logging spammed from everything using KRunner::RunnerManager (e.g. krunner app, but also Plasma shell via kickoff applet).
@broulik @davidedmundson @apol
Would also ask to have this included into 5.72 tarballs still.