Adapt to signature change of ROOT6 function ExecuteWithArgsAndReturn

IMPORTANT NOTE:  This pull request is to be merged concurrently with updating ROOT6 to its git HEAD
(commit 9bd887213b40a70db3a8f14362b8804506d5b384 or later), and updating the CMS specific ROOT6 patch
to ~wmtan/public/root6_patch_v1_for_v5-99-06-201-g9bd8872.patch.

Please update ROOT6 to the HEAD, update to the new patch, and merge this pull request all for the same IB.
The changes are mutually dependent.