ARROW-14796: [Python] Documentation: Correct default value
ARROW-14796: [Python] Documentation: Correct default value

This PR corrects the default value in the documentation text for the Python function `to_string`.

Jira ARROW-14796

Closes #11762 from zois-tasoulas/patch-1

Authored-by: zois <c76245543c264a9363913bd207ad50a6709e5205@users.noreply.github.com>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

apache/arrow,icexelloss/arrow,apache/arrow,apache/arrow,kou/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,icexelloss/arrow,kou/arrow,kou/arrow,kou/arrow,wesm/arrow,apache/arrow,apache/arrow,icexelloss/arrow,wesm/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,wesm/arrow,kou/arrow,apache/arrow,kou/arrow,apache/arrow,apache/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,laurentgo/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,apache/arrow,icexelloss/arrow,icexelloss/arrow,kou/arrow,laurentgo/arrow,kou/arrow,apache/arrow,apache/arrow,apache/arrow,kou/arrow,laurentgo/arrow,icexelloss/arrow,wesm/arrow,kou/arrow,kou/arrow,kou/arrow,apache/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,icexelloss/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,apache/arrow,kou/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,wesm/arrow,wesm/arrow,wesm/arrow,icexelloss/arrow