samples: display: lvgl: test sample with 'seeed_xiao_round_display'

This shield is compatible with all XIAO boards. Tested with 2 of them:
 * xiao_ble
 * xiao_esp32s3

Extend sample.yaml for integration testing with both, so there is coverage
across two very distinct SoC vendors and architectures.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>