Minor: Fix compiler warning when compiling datafusion-cli

[2010YOUY01]

Which issue does this PR close?

• Closes #.

Rationale for this change

When compiling datafusion-cli with cargo run, there is a compiler warning:

warning: unused variable: `options`
   --> datafusion/datasource-parquet/src/reader.rs:247:9
    |
247 |         options: Option<&'a ArrowReaderOptions>,
    |         ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_options`
    |
    = note: `#[warn(unused_variables)]` on by default

This PR uses #[allow(unused_variables)] to suppress the warning.

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[zhuqi-lucas]

LGTM Thank you @2010YOUY01 !