[Telemetry] Data-classification export pipeline failing this week - CI source connection needs re-auth

### Summary
The scheduled automation that exports azd telemetry events/fields and publishes them to the GDPR data-classification catalog has started failing this week. While it's down, telemetry classifications are not being refreshed.

### Symptom
Every scheduled run fails at the source-resolution stage - before any step executes - with an error that it cannot resolve its source branch (`refs/heads/main`).

### Analysis
- `main` is present and healthy, so this is not a missing-ref problem.
- Failing before any step runs, plus being unable to read its own source, points to the pipeline's CI source connection no longer authenticating (broken/deauthorized) - not a code or config change (config has been unchanged for months).
- The break window coincides with an internal CI identity/connection migration, which can invalidate existing connections.

### Impact
- GDPR telemetry event/field classifications are not updated or published while the pipeline is down.
- No runtime impact to azd itself; this is compliance/tooling automation.

### Proposed fix
1. Re-authorize (or recreate) the pipeline's source connection and re-run.
2. Add failure alerting - since failures occur before any in-pipeline step, alerting must be at the CI level (a YAML failure step won't fire).

### Status
I'm reaching out to the service connection owner to investigate this error; will update here once we have root cause / a fix.