Crash at exit if there's active net.box connection in application thread

Bug description

If an application thread has an active connection when Tarantool exits, an assertion failure occurs:

tarantool: ./src/box/lua/net_box.c:571: netbox_transport_destroy: Assertion `transport->worker == NULL' failed.

Reproduced with a debug build of Tarantool 3.8.0-entrypoint-67-g210970c87815. Tarantool 3.7 is likely to be affected as well.

Steps to reproduce

Create a listening Tarantool instance:

box.cfg{listen = 3301}

In another terminal, run the following script:

box.cfg{app_threads = 1}
require('experimental.threads').eval('app', [[
    require('net.box').connect(3301)
]])
os.exit(0)

Actual behavior

Tarantool crashes with an asserion failure.

Expected behavior

Tarantool exits without errors.

Start in src/box/lua/net_box.c around netbox_transport_destroy and reproduce the assertion with the Lua script in the issue using a debug build. Trace shutdown with an active net.box connection in an application thread, then verify that the same reproduction exits without errors.