`isolated_filesystem()` is not thread safe

[kdeldycke]

This is a follow-up on #2899, to cover for @Rowlando13's concerns that isolated_filesystem() is not thread safe: #2899 (comment)

[davidism]

Reminder that we should probably deprecate isolated_filesystem, there's a discussion about that somewhere around here.

[kdeldycke]

Reminder that we should probably deprecate isolated_filesystem, there's a discussion about that somewhere around here.

Found it at: #3123 (comment)

[kdeldycke]

BTW it looks like the original proposal by @bphunter1972 in #3123 of a runner.set_filesystem context manager seems to address the thread-safety as each runner will produce its artefacts and assets in its own directory on CLI invokation.