[Backport to 3.4] Remove most _CCCL_GRID_CONSTANT annotations, including merge sort - #9864

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: tibdex/github-app-token@v1.8.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/