What Does This Do

• Extracts shared GitLab test-job setup into .test_job_common for AMD64 and ARM64 jobs.
• Deduplicates the test-agent service configuration used by both architectures.
• Keeps ARM64 jobs gated on the AMD64 build job without downloading its platform-specific artifacts.
• Keeps the ARM64 default JVM subset manual on feature branches while retaining the full ARM64 matrix on merge queue and master.

Motivation

The ARM64 test templates duplicated most of the AMD64 Gradle setup, scripts, report collection, artifacts, retries, and test-agent configuration. That duplication made the architectures prone to drifting whenever shared CI setup changed and made rebases unnecessarily conflict-prone.

Sharing the common template keeps both architectures aligned. The AMD64 build gate also avoids spending ARM64 runner capacity on commits that do not compile.

Additional Notes

• ARM64 jobs remain non-blocking while stability data is collected.
• IBM Java 8 remains excluded because no ARM64 image is available; Oracle Java 8 remains excluded because it is too flaky for CI.
• Relevant precedents: #11364, #11470, and #11835.
• Validation: local YAML parsing and git diff --check passed; the repository commit hook completed its Gradle/Spotless checks successfully (6,534 tasks).

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, migration, or deletion
• Update public documentation with any new configuration flags or behaviors
• Once approved, use merge queue to merge the PR

Jira ticket: N/A