message: Add scalar tests for median
diff: statement ok
  PRAGMA enable_verification
  +# scalar quantiles
  +query II
  +SELECT median(NULL), median(1)
  +----
  +NULL 1
  +
  +query II
  +SELECT median(NULL), median(1) FROM range(2000)
  +----
  +NULL 1
  +
  statement ok
  create table quantile as select range r, random() from range(10000) union all values (NULL, 0.1), (NULL, 0.5), (NULL, 0.9) order by 2;
  