[AIROCMLIR-604] [DRAFT] Fix CK build/benchmarking tests in Nightly CI

[justinrosner]

Motivation

This PR addresses a build error that was causing the CK nightly comparison to fail, and then also makes sure that any errors are caught and noticeable to the CI (instead of always showing as green).

This implements: https://amd-hub.atlassian.net/browse/AIROCMLIR-604

Technical Details

• Disable CK unit tests during nightly benchmark builds by adding -DBUILD_TESTS=OFF to the CK cmake options. The nightly pipeline only needs CK's libraries install for benchmarking (it doesn't need the CK test suite)
• Replace catchError(buildResult: null) with catchError(buildResult: 'UNSTABLE', stageResult: 'FAILURE'). The previous setting silently swallowed all failures, leaving the overall build green even when the CK stage was completely broken. With this change, the stage is marked as FAILURE (red in stage view) and the build is marked as UNSTABLE (yellow), making CK-related issues visible without failing the entire nightly run

Test Plan

• Run the Nightly CI to make sure that the CK stage is now building successfully.

Test Result

• Verify that the CK stage is running successfully and that the benchmarking artifacts are created successfully

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.