vdiffr visual regression tests not working

[Ryo-N7]

possibly due to: r-lib/vdiffr#36

[Sayani07]

Any brainstorming on this would be helpful.
Some of the plot components depend on random variation which might lead to this problem as suggested here. The calc.falpha argument used in HDRs do use sampling. Maybe adding an seed here might help. Any suggestions?

[mitchelloharawild]

Closing as tests now seem fine. Presumably adding the seed fixed this issue.