fix(ci): relax the check when retain_paths is unset

If retain_paths is unset, the -eq comparison complains that it's not a
number. Using [[ ]] relaxes this and produces the expected result.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I556eab309ccc4d59d0a28c3a46a79be4229f96bc
1 file changed