Bug#914731: r-bioc-biocparallel: autopkgtest regression

[Graham Inggs]

Control: severity -1 important

Downgrading severity, since the autopkgtests now pass in unstable [1],
to avoid autoremoval warnings in several other packages.

[1] https://ci.debian.net/packages/r/r-bioc-biocparallel/unstable/amd64/