[user_events] Upgrade main to 1.18.0 (open-telemetry#496)

Author: ThomsonTan

.github/workflows/user_events.yml

@@ -27,7 +27,7 @@ jobs:
         uses: actions/checkout@v3
         with:
           repository: "open-telemetry/opentelemetry-cpp"
-          ref: "v1.17.0"
+          ref: "v1.18.0"
           path: "opentelemetry-cpp"
           submodules: "recursive"
       - name: setup dependencies