Environment.SetEnvironmentVariable/GetEnvironmentVariable mutate the
process-wide environ; concurrent setenv/getenv across parallel xunit test
classes is a documented crash/flake source on glibc even with unique
variable names. Group the six classes that touch process env vars into a
DisableParallelization=true collection so they run serially against each
other while everything else keeps running in parallel.
Joseph Doherty
1b65e820fb