Never run the root-cause agent on pull_request

The model costs real tokens and a PR only needs to prove the detection half
works. Gate root-cause on github.event_name != 'pull_request'; use
workflow_dispatch to exercise it once the workflow is on the default branch.

Author: atalman

.github/workflows/vllm-torch-nightly-triage.yml

@@ -102,9 +102,15 @@ jobs:
   # vllm-pytorch-ci-triage skill. Unprivileged: Bedrock via OIDC, no write scopes, and
   # no Buildkite or ClickHouse credentials -- the logs it reads were fetched upstream,
   # so the model only needs Read. Reports to the run summary; files nothing.
+  #
+  # Never runs on pull_request: the model costs real tokens and a PR only needs to
+  # prove the detection half works. Use workflow_dispatch to exercise this job.
   root-cause:
     needs: triage
-    if: needs.triage.outputs.has_report == 'true' && needs.triage.outputs.log_count != '0'
+    if: |
+      github.event_name != 'pull_request' &&
+      needs.triage.outputs.has_report == 'true' &&
+      needs.triage.outputs.log_count != '0'
     runs-on: ubuntu-24.04
     environment: bedrock
     timeout-minutes: 30