test: fix out-of-bound reads from invalid sizeof usage

`sizeof(data)` does not return the correct result here, as it measures
the size of the `data` variable, not what it points to.

PR-URL: #33115
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

test/addons/worker-buffer-callback/binding.cc

@@ -28,7 +28,7 @@ void Initialize(Local<Object> exports,
                node::Buffer::New(
                    isolate,
                    data,
-                   sizeof(data),
+                   sizeof(char),
                    [](char* data, void* hint) {
                      free_call_count++;
                    },

test/node-api/test_worker_buffer_callback/test_worker_buffer_callback.c

@@ -32,7 +32,7 @@ NAPI_MODULE_INIT() {
   NAPI_CALL(env, napi_create_external_arraybuffer(
       env,
       data,
-      sizeof(data),
+      sizeof(char),
       finalize_cb,
       NULL,
       &buffer));