twister: Always change skip to error on integration platforms

Before only with --integration such skips were changed to errors.
This hinders issues when twister is call with --all flag in CI
and new skips on integration platforms are not caught. Then those
skips cause errors in other PRs when --integration was used.

Signed-off-by: Maciej Perkowski <Maciej.Perkowski@nordicsemi.no>