Fix broken spec covering non-tar backups

What does this MR do?

Fixes a broken test that covers non-tarred backup files.

Previously, the test was passing because the it was nested within before, which prevented the typo from triggering an error. Once that was resolved, it highlighted that the test also didn't correctly cover the scenario it was supposed to (and was incorrectly passing) because it was hitting an unhandled exit 1.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation ([if required](https://docs.gitlab.com/ee/development/documentation/workflow.html#when-documentation-is-required))
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done