ci: Prevent inadvertent local files deletion in scripts/rspec_helpers.sh

What does this MR do and why?

I inadvertently deleted files on my computer when trying to run the update_tests_metadata locally. Since some CI env variables aren't set, we would run rm -rf /**/*! 😱

By default such env variable to a value of a folder that doesn't exist will result in an error thrown instead of an unwanted mass-deletion of files! 😅

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