Add no_sanitize to test_externref (emscripten-core#21715)

.s files cannot be sanitized.

Author: aheejin

test/test_core.py

@@ -9562,6 +9562,7 @@ def test_em_async_js(self):
 
   @requires_v8
   @no_wasm2js('wasm2js does not support reference types')
+  @no_sanitize('.s files cannot be sanitized')
   def test_externref(self):
     self.run_process([EMCC, '-c', test_file('core/test_externref.s'), '-o', 'asm.o'] + self.get_emcc_args(compile_only=True))
     self.emcc_args += ['--js-library', test_file('core/test_externref.js')]