message: fix(modal): fix button position in full width mode
  This change fixes button position of
  `<dds-modal expressive-size="full-width">`.
  There was a redundant style rule that had an adverse effect.
  Refs
diff: height: auto;
  }
  - ::slotted(#{$dds-prefix}-modal-body) {
  - min-height: carbon--rem(500px);
  - }
  -
  ::slotted(#{$dds-prefix}-lightbox-media-viewer-body) {
  height: 100%;
  overflow: auto;
  