tests/unit: Include 'qemu/main-loop.h' header in test-util-sockets.c

test-util-sockets.c calls qemu_init_main_loop(), itself declared in the "qemu/main-loop.h" header. Include the latter to avoid when refactoring unrelated headers: ../tests/unit/test-util-sockets.c:553:5: error: call to undeclared function 'qemu_init_main_loop' 553 | qemu_init_main_loop(&error_abort); | ^ Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-Id: <20260812211708.92824-4-philmd@oss.qualcomm.com>