Workaround TSAN CI bug

fix #2499

test/extras/include/boost/beast/test/yield_to.hpp

@@ -122,15 +122,21 @@ void
 enable_yield_to::
 spawn(F0&& f, FN&&... fn)
 {
-    asio::spawn(ioc_,
-        [&](yield_context yield)
+    // dispatch of spawn is a workaround for
+    // https://github.com/boostorg/beast/issues/2499
+    asio::dispatch(ioc_, 
+        [&]
         {
-            f(yield);
-            std::lock_guard<std::mutex> lock{m_};
-            if(--running_ == 0)
-                cv_.notify_all();
-        }
-        , boost::coroutines::attributes(2 * 1024 * 1024));
+            asio::spawn(ioc_,
+                [&](yield_context yield)
+                {
+                    f(yield);
+                    std::lock_guard<std::mutex> lock{m_};
+                    if(--running_ == 0)
+                        cv_.notify_all();
+                }
+                , boost::coroutines::attributes(2 * 1024 * 1024));
+        });
     spawn(fn...);
 }