fix async runtime test

Author: lalitb

opentelemetry-sdk/src/trace/runtime_tests.rs

@@ -25,7 +25,7 @@ struct SpanCountExporter {
 
 #[cfg(any(feature = "rt-tokio", feature = "rt-tokio-current-thread"))]
 impl SpanExporter for SpanCountExporter {
-    async fn export(&mut self, batch: Vec<crate::trace::SpanData>) -> OTelSdkResult {
+    async fn export(&self, batch: Vec<crate::trace::SpanData>) -> OTelSdkResult {
         self.span_count.fetch_add(batch.len(), Ordering::SeqCst);
         Ok(())
     }

opentelemetry-sdk/src/trace/span_processor_with_async_runtime.rs

@@ -457,7 +457,7 @@ mod tests {
         D: Fn(Duration) -> DS + 'static + Send + Sync,
         DS: Future<Output = ()> + Send + Sync + 'static,
     {
-        async fn export(&mut self, _batch: Vec<SpanData>) -> OTelSdkResult {
+        async fn export(&self, _batch: Vec<SpanData>) -> OTelSdkResult {
             (self.delay_fn)(self.delay_for).await;
             Ok(())
         }