fix: fastify ERR_HTTP_HEADERS_SENT is reply is not awaited

[vafanassieff]

Hey there,

I was trying to use trpc-openapi with fastify-session, and I was wondering why I have ERR_HTTP_HEADERS_SENT when sending request to trpc-openapi.

I found that @mgcrea/fastify-session tried to save multiple times the session.

fastify reply.send call must be awaited to ensure the request is done.

[vafanassieff]

@jlalmes Is there anything I can do help you ?