Admin: Adjust select2 multiple initial height
Admin: Adjust select2 multiple initial height

Make select2 multiple default height more in line with other form inputs.

Refs SHUUP-3158

shawnadelic/shuup,shoopio/shoop,suutari-ai/shoop,suutari/shoop,shoopio/shoop,hrayr-artunyan/shuup,suutari-ai/shoop,shawnadelic/shuup,suutari-ai/shoop,hrayr-artunyan/shuup,hrayr-artunyan/shuup,shawnadelic/shuup,suutari/shoop,suutari/shoop,shoopio/shoop