fix(telemetry): allowlist xrpl_work_item as an external infra label

check-otel-naming fails Rule D on this branch: ledger-data-sync.json
aggregates by xrpl_work_item, which nothing in-tree emits because
perf-iac's alloy pipeline stamps it, so it cannot be derived from
*SpanNames.h. The sibling perf-iac identities xrpl_branch and
xrpl_node_role are already allowlisted; this one was missed when the
by() clauses were reintroduced.

Add it to EXTERNAL_INFRA_LABELS alongside them. Verified by removing
the entry again, which restores the failure.

.github/scripts/otel-naming/check_otel_naming.py

@@ -818,6 +818,7 @@ def metric_label_names(root: Path) -> Set[str]:
 # repo's OTel code (never as a workaround for a dashboard querying a label
 # that nothing actually emits — that is a real Rule D violation).
 EXTERNAL_INFRA_LABELS = {
+    "xrpl_work_item",  # perf-iac: ticket/work-item id for the perf comparison run
     "xrpl_branch",  # perf-iac: git ref of the xrpld build under test
     "xrpl_node_role",  # perf-iac: validator/peer role in the perf cluster
 }