Update the directory for unshifting

What does this MR do?

Resolves broken master for update-test-metadata due to !23335 (merged) which updated the directory of prune-old-examples but did not update the relative __dir__ reference.

This did not cause a failure in the MR Pipeline because update-test-metadata only runs on scheduled pipelines.

Screenshots

Local run before change:

Local run after change:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #198274 (closed)