When bitcoin-gui is built against OpenBSD's system Qt packages (which
have GLib support), shutdown emits "GLib-CRITICAL **:
g_main_context_pop_thread_default: assertion 'stack != NULL' failed"
messages on stderr, which the test framework treats as a failure.
Set `QT_NO_GLIB=1` so Qt falls back to its poll-based event dispatcher,
which avoids the GLib thread-default context entirely.