Fix clippy failures: error: use of deprecated function `functions::make_scalar_function

[alamb]

Which issue does this PR close?

Closes #8973

Rationale for this change

CI checks are failing on main: https://github.com/apache/arrow-datafusion/actions/runs/7628515989/job/20779877406

error: use of deprecated function `functions::make_scalar_function`: Implement your function directly in terms of ColumnarValue or use `ScalarUDF` instead
   --> datafusion/physical-expr/src/functions.rs:562:17
    |
562 |                 make_scalar_function(string_expressions::instr::<i32>)(args)
    |                 ^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D deprecated` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(deprecated)]`

I believe this is a logical conflict between #8862 and #8878

What changes are included in this PR?

Fix logical conflicts

Are these changes tested?

yes

Are there any user-facing changes?

[alamb]

Thanks @viirya