.pullapprove.yml: Switch to v2 and other updates
.pullapprove.yml: Switch to v2 and other updates

This lazily copies image-spec's configuration as updated via
https://github.com/opencontainers/project-template/pull/29 and
https://github.com/opencontainers/image-spec/pull/616

Signed-off-by: Jonathan Boulle <0d47477beef1d882e8812885f3dcf66c4a47c346@gmail.com>

opencontainers/image-tools,opencontainers/image-tools