chore: Store integration-test artifacts for a week

What does this MR do?

Stores gl-sast-report.json files generated by the integration-test job for a week. This will aid in debugging test failures and reduces the need to run integration tests locally to update expectation files.

Browse them here: https://gitlab.com/gitlab-org/security-products/analyzers/semgrep/-/jobs/3983130793/artifacts/browse/tmp/test-13878/

Direct port of secrets!207 (merged)

What are the relevant issue numbers?

N/A

Does this MR meet the acceptance criteria?

• Changelog entry added
• Conforms to the code review guidelines
• Security reports checked/validated by reviewer