math/R-cran-RcppParallel: Update 6.0.0 => 6.1.1

Changelog:
https://github.com/RcppCore/RcppParallel/blob/v6.1.1/NEWS.md

PR: 297110
Reported by: Christos Longros <chris.longros@gmail.com> (maintainer)
Approved by: osa, vvd (Mentors, implicit)
MFH: 2026Q3