cleanup(otel): suppress maybe unitialized warning (googleapis#14343)

* cleanup(otel): suppress maybe unitialized warning

* address review comments

Author: dbolduc

google/cloud/internal/opentelemetry.h

@@ -242,11 +242,12 @@ bool TracingEnabled(Options const& options);
 template <typename Rep, typename Period>
 std::function<void(std::chrono::duration<Rep, Period>)> MakeTracedSleeper(
     Options const& options,
-    std::function<void(std::chrono::duration<Rep, Period>)> const& sleeper,
+    std::function<void(std::chrono::duration<Rep, Period>)> sleeper,
     std::string const& name) {
 #ifdef GOOGLE_CLOUD_CPP_HAVE_OPENTELEMETRY
   if (TracingEnabled(options)) {
-    return [=](std::chrono::duration<Rep, Period> d) {
+    return [name, sleeper = std::move(sleeper)](
+               std::chrono::duration<Rep, Period> d) {
       // A sleep of 0 is not an interesting event worth tracing.
       if (d == std::chrono::duration<Rep, Period>::zero()) return sleeper(d);
       auto span = MakeSpan(name);