Hello, there. Run into the problem with DISTINCT expression. It works incorrectly on the main query if it was already applied to one of the subqueries bond with UNION ALL.

**How to reproduce**
Server version: 20.5.4.40. 19.17.6.36 was free of the bug.
Using Datagrip for running queries.
Non-default settings:
```
input_format_defaults_for_omitted_fields: 1
decimal_check_overflow: 0
joined_subquery_requires_alias: 0
```

Consider following query
```
select distinct number
from ((select number from numbers(10)) union all (select number from numbers(20)));
```
It works fine, returning 20 rows as expected.

But if we add distinct to subqueries (it doesn't matter to the first, the second or both)
```
select distinct number
from ((select distinct number from numbers(10)) union all (select distinct number from numbers(20)));
```

Then in 20.5.4.40 we'll see 30 rows with numbers from 0 to 9 duplicated.
However, `count(distinct number)` returns the correct number of rows.

{
    const FunctionFactory & function_factory = FunctionFactory::instance();
    if (!select_query->groupBy())
    {
        
        if (select_query->having())
            appendUnusedGroupByColumn(select_query, source_columns);
        return;
    }
    const auto is_literal = [] (const ASTPtr & ast) -> bool
    {
        return ast->as<ASTLiteral>();
    };
    auto & group_exprs = select_query->groupBy()->children;
    
    const auto remove_expr_at_index = [&group_exprs] (const size_t idx)
    {
        if (idx < group_exprs.size() - 1)
            std::swap(group_exprs[idx], group_exprs.back());
        group_exprs.pop_back();
    };
    
    for (size_t i = 0; i < group_exprs.size();)
    {
        if (const auto * function = group_exprs[i]->as<ASTFunction>())
        {
            
            if (possibly_injective_function_names.count(function->name))
            {