chore: use new testing-tools image

[dervoeti]

Description

Part of stackabletech/issues#767

This uses the new oci.stackable.tech/sdp/testing-tools image (0.3.0).

Ran some tests to verify they still work:

--- PASS: kuttl (38.05s)
--- PASS: kuttl/harness (0.00s)
--- PASS: kuttl/harness/smoke_opa-1.8.0_openshift-false_use-tls-false (38.02s)

--- PASS: kuttl (51.88s)
--- PASS: kuttl/harness (0.00s)
--- PASS: kuttl/harness/logging_opa-1.8.0_openshift-false (37.69s)
--- PASS: kuttl/harness/logging_opa-1.4.2_openshift-false (51.87s)

--- PASS: kuttl (32.92s)
--- PASS: kuttl/harness (0.00s)
--- PASS: kuttl/harness/openldap-user-info_opa-latest-1.8.0_openshift-false (32.91s)

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible
• Links to generated (nightly) docs added
• Release note snippet added

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker