Fix ArrayAgg schema mismatch issue

[jayzhan211]

Which issue does this PR close?

Closes #8032.

Rationale for this change

The main issue for #8032 is as what the errors said we have different schema for result.schema which is logical-expr schema and results.collect()[0].schema which is physical-expr schema.

We should have the same is_nullable for both logical-expr and physical-expr

We can see that the logical-expr of List is set with expr.nullable(schema)
https://github.com/apache/arrow-datafusion/blob/3469c4e09a3d32381949dd0c0f626f406c00c6ad/datafusion/expr/src/expr_schema.rs#L289-L305
and logical-expr of List element is set with the return type of Aggregatefunciton::ArrayAgg
https://github.com/apache/arrow-datafusion/blob/3469c4e09a3d32381949dd0c0f626f406c00c6ad/datafusion/expr/src/aggregate_function.rs#L286-L290

What changes are included in this PR?

Fix schema is_nullable

Are these changes tested?

I did not test end to end like #8032 , just make sure the schema is the same.

Are there any user-facing changes?

[alamb]

Thank you @jayzhan211 -- it would be nice if there was some way to avoid having to plumb the is_expr_nullable flag through, but I don't think there is

[alamb]

Thank you @jayzhan211 for the contribution and working on this area of the code

[alamb]

Thanks again @jayzhan211