fix: use array format with x-sentry-auth header for Sentry OTLP

Switch from flat object format (OTEL_EXPORTER_OTLP_HEADERS) to array
format with explicit x-sentry-auth header name, matching what Sentry's
OTLP endpoint expects per their docs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lpcox

.github/workflows/smoke-otel-tracing.lock.yml

@@ -11,8 +11,10 @@ permissions:
 
 observability:
   otlp:
-    endpoint: ${{ secrets.GH_AW_OTEL_SENTRY_ENDPOINT }}
-    headers: ${{ secrets.GH_AW_OTEL_SENTRY_AUTHORIZATION }}
+    endpoint:
+      - url: ${{ secrets.GH_AW_OTEL_SENTRY_ENDPOINT }}
+        headers:
+          x-sentry-auth: ${{ secrets.GH_AW_OTEL_SENTRY_AUTHORIZATION }}
 
 engine:
   id: copilot