added missing test for the MultiTrajectory`s staticVariables
Follow-up addition related to !66631 (merged) @tbold
Similar approach to TrackSummaryContainer
related test
related to EFTRACK-325
Edited by Ioannis Maznas
Follow-up addition related to !66631 (merged) @tbold
Similar approach to TrackSummaryContainer
related test
related to EFTRACK-325