Spurious cast to Uint8 inserted when coalesce is used in a context of a join

### Describe the bug

Following is a valid (as far as I can tell) SQL that blows up in DataFusion:

```
DataFusion CLI v20.0.0
❯ with customer as (
select 11111 as c_custkey
), cust as (
select case when c_custkey = 0 then null else c_custkey end as c_custkey from customer
)
select coalesce(a.c_custkey, b.c_custkey) as custkey
from cust a inner join cust b
on a.c_custkey = b.c_custkey;
Arrow error: Cast error: Can't cast value 11111 to type UInt8
```

The culprit seems to be a spurious cast to UInt8 that gets inserted in coalesce arguments:

```
❯ explain with customer as (
select 11111 as c_custkey
), cust as (
select case when c_custkey = 0 then null else c_custkey end as c_custkey from customer
)
select coalesce(a.c_custkey, b.c_custkey) as custkey
from cust a inner join cust b
on a.c_custkey = b.c_custkey;
+---------------+----------------------------------------------------------------------------------------------------------------------------------------------+
| plan_type | plan |
+---------------+----------------------------------------------------------------------------------------------------------------------------------------------+
| logical_plan | Projection: coalesce(CAST(a.c_custkey AS UInt8), CAST(b.c_custkey AS UInt8)) AS custkey |
| | Inner Join: a.c_custkey = b.c_custkey |
| | SubqueryAlias: a |
| | SubqueryAlias: cust |
| | Projection: CASE WHEN customer.c_custkey = Int64(0) THEN Int64(NULL) ELSE customer.c_custkey END AS c_custkey |
| | SubqueryAlias: customer |
| | Projection: Int64(11111) AS c_custkey |
| | EmptyRelation |
| | SubqueryAlias: b |
| | SubqueryAlias: cust |
| | Projection: CASE WHEN customer.c_custkey = Int64(0) THEN Int64(NULL) ELSE customer.c_custkey END AS c_custkey |
| | SubqueryAlias: customer |
| | Projection: Int64(11111) AS c_custkey |
| | EmptyRelation |
...
```

### To Reproduce

See above repro in the CLI

### Expected behavior

The query above is expected to succeed

### Additional context

Any simplification to the above query I tried (e.g. removing join, case, or coalesce) makes the issue go away.

E.g. here is a query where b.custkey is replaced by 0 in the coalesce call:

```
❯ with customer as (
select 11111 as c_custkey
), cust as (
select case when c_custkey = 0 then null else c_custkey end as c_custkey from customer
)
select coalesce(a.c_custkey, 0) as custkey
from cust a inner join cust b
on a.c_custkey = b.c_custkey;
+---------+
| custkey |
+---------+
| 11111 |
+---------+
1 row in set. Query took 0.021 seconds.
```

Run the reproducer in the DataFusion CLI and compare its output with the EXPLAIN plan, focusing on the UInt8 casts added to coalesce arguments after the join. Trace the logical-plan and type-coercion path that produces that plan, then add a regression test for the query and verify it succeeds without the spurious cast.

Written by the indexing model from the issue text.