nixos/tests: update nginx-http3 test

    server.wait_for_open_port(443)

    # Check http connections

    client.succeed("curl --verbose --http3 https://acme.test | grep 'Hello World!'")

    client.succeed("curl --verbose --http3-only https://acme.test | grep 'Hello World!'")

    # Check downloadings

    client.succeed("curl --verbose --http3 https://acme.test/example.txt --output /tmp/example.txt")

    client.succeed("curl --verbose --http3-only https://acme.test/example.txt --output /tmp/example.txt")

    client.succeed("cat /tmp/example.txt | grep 'Check http3 protocol.'")

    # Check header reading

    client.succeed("curl --verbose --http3 --head https://acme.test | grep 'content-type'")

    client.succeed("curl --verbose --http3 --head https://acme.test | grep 'HTTP/3 200'")

    client.succeed("curl --verbose --http3 --head https://acme.test/error | grep 'HTTP/3 404'")

    client.succeed("curl --verbose --http3-only --head https://acme.test | grep 'content-type'")

    client.succeed("curl --verbose --http3-only --head https://acme.test | grep 'HTTP/3 200'")

    client.succeed("curl --verbose --http3-only --head https://acme.test/error | grep 'HTTP/3 404'")

    # Check change User-Agent

    client.succeed("curl --verbose --http3 --user-agent 'Curl test 3.0' https://acme.test")

    client.succeed("curl --verbose --http3-only --user-agent 'Curl test 3.0' https://acme.test")

    server.succeed("cat /var/log/nginx/access.log | grep 'Curl test 3.0'")

    server.shutdown()