autopkgtest fails in Impish

[Balint Reczey]

https://autopkgtest.ubuntu.com/packages/r/r-cran-treescape/impish/s390x

https://autopkgtest.ubuntu.com/results/autopkgtest-impish/impish/s390x/r/r-cran-treescape/20210511_142554_7675d@/log.gz

...
> test_check("treescape")
2: 'rgl.init' failed, running with 'rgl.useNULL = TRUE'.
== Failed tests ================================================================
-- Failure (testbasics.R:45:3): treeDist equals corresponding entry of multiDist --
treeDist(trees[[1]], trees[[2]]) not equal to multiDist(trees)[[1]].
Classes differ: numeric is not dist
-- Failure (testbasics.R:46:3): treeDist equals corresponding entry of multiDist --
treeDist(trees[[1]], trees[[2]], emphasise.tips = c("t1", "t2")) not equal to multiDist(trees, emphasise.tips = c("t1", "t2"))[[1]].
Classes differ: numeric is not dist
-- Failure (testbasics.R:58:3): multiDist equals the distance matrix from treescape --
multidistMatrixFunction(0)[[n]] not equal to treedistMatrix[[n]].
names for current but not for target
...