Fix CI check when version changes -- remove checked in file that is created by doc example

[alamb]

Which issue does this PR close?

Closes #11892

Rationale for this change

See #11892 -- basically if versions change the CI fails

The problem is that the output parquet file that is written as part of the doc example is checked in, and thus if the actual bytes written by the example change (e.g. when the version number changes) the local file is different too

What changes are included in this PR?

1. Delete the example.parquet file
2. Add it to .gitignore so it isn't added again
3. Update example to avoid recreating it

Are these changes tested?

Yes by CI

Are there any user-facing changes?

No, this is a test fix only

[korowa]

Since this file is produced by https://github.com/apache/datafusion/blob/main/docs/source/library-user-guide/using-the-dataframe-api.md#write-dataframe-to-files, which is runned by this doctest as

cargo test --doc 'library_user_guide_dataframe_api'

won't it be better to replace it with tempdir rather than adding this file to gitignore? E.g.

use datafusion::prelude::*;
use datafusion::error::Result;
use datafusion::dataframe::DataFrameWriteOptions;

#[tokio::main]
async fn main() -> Result<()> {
    // Replace with actual target path
    let target_path = tempfile::tempdir()?.path().join("example.parquet");

    let ctx = SessionContext::new();
    // read example.csv file into a DataFrame
    let df = ctx.read_csv("tests/data/example.csv", CsvReadOptions::new()).await?;
    // stream the contents of the DataFrame to the target file
    df.write_parquet(
        target_path.to_string_lossy().as_ref(),
        DataFrameWriteOptions::new(),
        None, // writer_options
    ).await;
    Ok(())
}

or to delete the file in the end of the example, like it's done in other doctests, but using tempdir has zero (or close to it) risk that this file will be committed.

[alamb]

won't it be better to replace it with tempdir rather than adding this file to gitignore? E.g.

Good idea -- thanks @korowa. Done in 14caf64

[korowa]

🚀

Thank you @alamb

[alamb]

Thank you for the review @korowa