Header Sync fails with new v25.0.0 header

[KevinEady]

The most recent Header Sync job failed: https://github.com/nodejs/node-api-headers/actions/runs/18546297503

Looks like an issue with the nested #ifdefs added for the "NAPI_EXPERIMENTAL is enabled" warning:

#if defined(NAPI_EXPERIMENTAL) &&                                              \
    !defined(NODE_API_EXPERIMENTAL_NO_WARNING) &&                              \
    !defined(NODE_WANT_INTERNALS)
#ifdef _MSC_VER
#pragma message("NAPI_EXPERIMENTAL is enabled. "                               \
                "Experimental features may be unstable.")
#else
#warning "NAPI_EXPERIMENTAL is enabled. " \
       "Experimental features may be unstable."
#endif
#endif