ci: temporarily make user-journey gate advisory

[rohita5l]

Summary

Temporarily make the User Journey Test Required check advisory while GitHub-hosted runner access is blocked by the Databricks organization IP allowlist (observed on #770).

• Add step-level continue-on-error: true to the existing judge invocation, so failures no longer fail the named job check.
• Keep the judge running and preserve its error annotations and logs. This makes all judge-step failures advisory, including missing-coverage verdicts, until enforcement is restored.
• Keep the workflow/check names, trusted-base checkout, pull_request_target trigger, permissions, secrets, and waiver workflow unchanged.

This is a standalone three-line workflow change based on main; it does not include the code or CUJ changes from #770. It does not fix runner connectivity or change branch-protection settings. Remove the temporary tolerance once approved runner egress is available.

Validation

• Existing user-journey gate tests: 8 passed.
• YAML parse and semantic comparison: the only configuration change is step-level continue-on-error: true.
• git diff --check passed.
• Hosted execution has not been verified; pull_request_target uses the base-branch workflow, so this change takes effect only after landing on main and a fresh qualifying PR event. This PR's own check will still use the existing blocking workflow.