ci: use the `vtkm` for macOS runners
The existing vtk-m tag is still there to pick up old jobs. Will retire the old tag once supported release branches backport this change (either by becoming unmaintained or backporting this MR).
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The existing vtk-m tag is still there to pick up old jobs. Will retire the old tag once supported release branches backport this change (either by becoming unmaintained or backporting this MR).