*/*unit*: update NGINX Unit: 1.30.0 -> 1.31.0

<ChangeLog>

*) Change: if building with njs, version 0.8.0 or later is now required.

*) Feature: technology preview of WebAssembly application module.

*) Feature: "response_headers" option to manage headers in the action
  and fallback.

*) Feature: HTTP response header variables.

*) Feature: ASGI lifespan state support. Thanks to synodriver.

*) Bugfix: ensure that $uri variable is not cached.

*) Bugfix: deprecated options were unavailable.

*) Bugfix: ASGI applications inaccessible over IPv6.

</ChangeLog>

(osa)