stackruntime: Our fake telemetry span must be passed by pointer

Most of our Span actions don't mutate the object because we just
immediately emit messages to the test log, but SetName directly modifies
the span name so we need to pass by pointer so we can honor that rename.

internal/stacks/stackruntime/telemetry_test.go

@@ -178,7 +178,7 @@ func (t *testLogTracer) Start(ctx context.Context, spanName string, opts ...trac
 		TraceID: fakeTraceIDForTesting,
 		SpanID:  spanID,
 	})
-	span := testLogTraceSpan{
+	span := &testLogTraceSpan{
 		name:        spanName,
 		context:     &spanCtx,
 		t:           t.t,
@@ -210,7 +210,7 @@ type testLogTraceSpan struct {
 	embedded.Span
 }
 
-var _ trace.Span = testLogTraceSpan{}
+var _ trace.Span = (*testLogTraceSpan)(nil)
 
 func (s testLogTraceSpan) log(f string, args ...any) {
 	s.t.Helper()
@@ -263,7 +263,7 @@ func (s testLogTraceSpan) SetAttributes(kv ...attribute.KeyValue) {
 }
 
 // SetName implements trace.Span.
-func (s testLogTraceSpan) SetName(name string) {
+func (s *testLogTraceSpan) SetName(name string) {
 	s.t.Helper()
 	s.log("RENAMED to %s", name)
 	s.name = name