Missing WORKSPACE validation in run_tests.sh

[brianredbeard]

Description

The script uses WORKSPACE without checking if it's set, potentially causing errors or writing to unexpected locations.

Location

https://github.com/validatedpatterns/multicloud-gitops/blob/main/tests/interop/run_tests.sh

Expected Behavior

Check if WORKSPACE is set before use with ${WORKSPACE:-} syntax.