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 (107.59s)
--- PASS: kuttl/harness (0.00s)
--- PASS: kuttl/harness/smoke_superset-6.0.0-rc2_openshift-false (107.56s)

--- PASS: kuttl (579.69s)
--- PASS: kuttl/harness (0.00s)
--- PASS: kuttl/harness/opa_superset-4.0.2_opa-latest-1.8.0_openshift-false (297.65s)
--- PASS: kuttl/harness/opa_superset-4.1.4_opa-latest-1.8.0_openshift-false (333.39s)
--- PASS: kuttl/harness/opa_superset-6.0.0-rc2_opa-latest-1.8.0_openshift-false (232.78s)
--- PASS: kuttl/harness/opa_superset-4.1.2_opa-latest-1.8.0_openshift-false (246.29s)

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

[razvan]

lgtm