Re-disable test_pthread_dlopen_many under wasm64. NFC (#19495)

Author: sbc100

test/test_core.py

@@ -9425,6 +9425,9 @@ def test_pthread_dlopen(self):
   @needs_dylink
   @node_pthreads
   def test_pthread_dlopen_many(self):
+    if self.is_wasm64():
+     self.skipTest('https://github.com/emscripten-core/emscripten/issues/18887')
+
     nthreads = 10
     self.emcc_args += ['-Wno-experimental', '-pthread']
     self.build_dlfcn_lib(test_file('core/pthread/test_pthread_dlopen_side.c'))