autopkgtest fails in focal on amd64

[Balint Reczey]

The test used to be flaky periodically and it is passing consistently in Hirsute.

https://autopkgtest.ubuntu.com/packages/r/r-cran-processx/focal/amd64

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-focal/focal/amd64/r/r-cran-processx/20210106_102031_2a866@/log.gz
...
== Failed ======================================================================
-- 1. Error: ps methods (@test-ps-methods.R#13) -------------------------------
No such process, pid 2320, ???
Backtrace:
 1. testthat::expect_true(ps::ps_name(ps) %in% c("px", "px.exe")) test-ps-methods.R:13:2
 5. ps::ps_name(ps)
...

https://autopkgtest.ubuntu.com/packages/r-cran-processx/hirsute/amd64