[2.8] Add regression test for detach() on non-seekable streams

[eyupcanakman]

Stream::detach() used to call ftell(), feof(), and stream_get_meta_data()
on the resource after clearing the internal reference. On non-seekable stream types
(e.g. tcp_socket/ssl), ftell() raises a TypeError on PHP 8.

Those calls were removed from detach(), but no test covered this scenario.
Add a regression test using a popen pipe (non-seekable) to confirm detach()
returns the resource cleanly and leaves the Stream object in the expected
detached state.

Fixes #630.