Fix workspace sentry error for no key in referenced_command

MR - Fix bug with workspace devfile event command no... (!199388 - merged)

Description

• From Sentry on workspace alert channel, https://gitlab.slack.com/archives/C093VPLM53L/p1753424491652139

  🔴 NoMethodError undefined method `[]' for nil:NilClass (NoMethodError)

       next if referenced_command[:exec].present?
                                ^^^^^^^

  environment: gprd

And we would need to fix the bug in our code for unsafe hash key access for nil.

Acceptance criteria

• Fix the bug
• Add proper unit testing

Implementation plan

NA