ci: run knip-reporter on failure

[rndquu]

Check this CI run which failed with error Unable to download artifact(s): Artifact not found for name: knip-results.

It happened because knip workflow uploads results only on failure while knip-reporter workflow tries to download knip results every time. So when there are no knip errors the knip-reporter workflow tries to download an artifact that doesn't exist.

This PR runs knip-reporter workflow only if knip workflow failed. This way the knip results artifact is always present and the Unable to download artifact(s): Artifact not found for name: knip-results error is gone (along with github notifications).

QA (no knip errors):

• Knip: https://github.com/rndquu/conversation-rewards/actions/runs/9588457290/job/26440524402?pr=3
• Knip reporter: https://github.com/rndquu/conversation-rewards/actions/runs/9588463220

QA (with knip errors):

• Knip: https://github.com/rndquu/conversation-rewards/actions/runs/9588471702/job/26440570139?pr=3
• Knip reporter: https://github.com/rndquu/conversation-rewards/actions/runs/9588478757

[gitcoindev]

Makes sense! This case will indeed be fixed by this change.