Fuzzer: Run Asyncify less

scripts/fuzz_opt.py

diff --git a/scripts/fuzz_opt.py b/scripts/fuzz_opt.py
index e43d40d..dadd651 100755
--- a/scripts/fuzz_opt.py
+++ b/scripts/fuzz_opt.py
@@ -965,7 +965,9 @@
 
 
 class Asyncify(TestCaseHandler):
-    frequency = 0.6
+    # run this at low frequency for now, as there is at least one known long-
+    # standing issue, https://github.com/WebAssembly/binaryen/issues/4865
+    frequency = 0.06
 
     def handle_pair(self, input, before_wasm, after_wasm, opts):
         # we must legalize in order to run in JS