Ignore false positive only_used_in_recursion Clippy warning

[DerGut]

Which issue does this PR close?

Ignores a Clippy warning identified in #15625. Note, that this warning seems to be a false positive. I've submitted an issue with the Clippy project rust-lang/rust-clippy#14566. Ideally we'd get this fixed upstream instead of having to add this ignore directive.

Rationale for this change

As mentioned in #15625 (review), we get a Clippy warning

warning: parameter is only used in recursion
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:48:9
   |
48 |         config: &ConfigOptions,
   |         ^^^^^^ help: if this is intentional, prefix it with an underscore: `_config`
   |
note: parameter used here
  --> datafusion/physical-optimizer/src/aggregate_statistics.rs:86:42
   |
86 |                     self.optimize(child, config).map(Transformed::yes)
   |                                          ^^^^^^
...
91 |             plan.map_children(|child| self.optimize(child, config).map(Transformed::yes))
   |                                                            ^^^^^^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#only_used_in_recursion
   = note: `#[warn(clippy::only_used_in_recursion)]` on by default

when linting the datafusion-physical-optimizer crate: cargo clippy -p datafusion-physical-optimizer.

What changes are included in this PR?

No real change was possible, so I added an ignore directive.

Clippy suggests to prefix the config parameter with an underscore but it is still used in the function body to pass it to recursive calls. Removing the parameter was also not an option because it is defined on the PhysicalOptimizerRule trait and other implementations use it.

Are these changes tested?

Running cargo clippy -p datafusion-physical-optimizer now reports no warnings.

Are there any user-facing changes?

No, no actual code change.

[alamb]

Thanks @DerGut -- rust-lang/rust-clippy#14566 is an interesting report

[alamb]

Thank you @DerGut -- this is a great contribution

[alamb]

💯 for leaving context in comment