union distinct shouldn't have distinct on a different line

[tconbeer]

Discussed in #416

^{Originally posted by paschmaria May 4, 2023}
Describe the bug
distinct shouldn't be on the next line for union distinct

To Reproduce

select *
from table_a
union distinct
select *
from table_b

Expected behavior

select *
from table_a
union distinct
select *
from table_b

Actual behavior

select *
from table_a
union
distinct
select *
from table_b

Additional context

What is the output of sqlfmt --version?

sqlfmt, version 0.18.1