deps: fix indenting of sources in ngtcp2.gyp

PR-URL: https://github.com/nodejs/node/pull/34033


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>