Running just run on a product without PERSIST_LICENSE=true produces an error on macOS bash

[ianpittwood]

Reported by @vivas89

macOS bash doesn't seem to support the [@] expansion operator for empty arrays. When running just run on a product on macOS without PERSIST_LICENSE=true enabled produces the following error:

rstudio-docker-products $ just RSW_LICENSE="XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX" workbench/run 
echo "rstudio-workbench:ubuntu2204-$(just -f ../Justfile _get-tag-safe-version 2023.06.0+421.pro1)"
+ '[' -z XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX ']'
+ volume_opts=()
+ '[' false = true ']'
/var/folders/1n/phcn485d42g99_dfd47dqq700000gn/T/justvkeaNM/run: line 97: volume_opts[@]: unbound variable
error: Recipe `run` failed with exit code 1