[summarize-checks] Don't set duplicate statuses

[mikeharder]

I think summarize-checks can be optimized to not set duplicate statuses:

Statuses:
- Swagger Avocado: success
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- Swagger LintDiff: success
- [TEST-IGNORE] Automated merging requirements met: failure
- Swagger ApiDocPreview: pending
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Swagger ModelValidation: success
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Swagger SemanticValidation: success
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Automated merging requirements met: failure
- [TEST-IGNORE] Swagger ModelValidation: pending
- [TEST-IGNORE] Swagger SemanticValidation: pending
- Swagger Avocado: pending
- Breaking Change(Cross-Version): pending
- Swagger BreakingChange: pending
- Swagger LintDiff: pending

https://github.com/Azure/azure-rest-api-specs-pr/actions/runs/16824055949/job/47656466045

const existingStatus = getStatus(AMRM);
if (existingStatus != newStatus) {
  github.rest.setStatus(AMRM, newStatus);
} else {
  info("no change");
}