Ruby: Handle response field arrays

@xeron on GitHub reported an issue whereby with a Rails 7.1 application
they were getting the following error

  2023/10/22 20:57:28 [error] 56#56 [unit] #8: Ruby: Wrong header entry 'value' from application
  2023/10/22 20:57:28 [error] 56#56 [unit] #8: Ruby: Failed to run ruby script

After some back and forth debugging it turns out rack was trying to send
back a header comprised of an array of values. E.g

  app = Proc.new do |env|
      ["200", {
          "Content-Type" => "text/plain",
          "X-Array-Header" => ["Item-1", "Item-2"],
      }, ["Hello World\n"]]
  end

  run app

It seems this became a possibility in rack v3.0[0]

So along with a header value type of T_STRING we need to also allow
T_ARRAY.

If we get a T_ARRAY we need to build up the header field using the given
values.

E.g

  "X-Array-Header" => ["Item-1", "", "Item-3", "Item-4"],

becomes

  X-Array-Header: Item-1; ; Item-3; Item-4

[0]: <https://github.com/rack/rack/blob/main/UPGRADE-GUIDE.md?plain=1#L26>

Reported-by: Ivan Larionov <xeron.oskom@gmail.com>
Closes: <https://github.com/nginx/unit/issues/974>
Link: <https://github.com/nginx/unit/pull/998>
Tested-by: Timo Stark <t.stark@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

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