fix: use datafusion_expr instead of datafusion crate - #22052

Which issue does this PR close?

• N/A

Rationale for this change

• Building the datafusion-spark crate in isolation, e.g. cargo clippy -p datafusion-spark fails as indicated by fix: use datafusion_expr instead of datafusion crate in spark  #21043

error[E0433]: failed to resolve: use of unresolved module or unlinked crate `datafusion`
  --> datafusion/spark/src/function/string/is_valid_utf8.rs:19:5
   |
19 | use datafusion::logical_expr::{ColumnarValue, Signature, Volatility};
   |     ^^^^^^^^^^ use of unresolved module or unlinked crate `datafusion`

What changes are included in this PR?

Fix import statement. No code changes.

Are these changes tested?

Yes, building datafusion-spark crate works now.

Are there any user-facing changes?

N/A