Add missing BashOperator import to documentation example

[tadeha]

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This pull request addresses an issue in the Airflow documentation where the BashOperator was used in a code example but not imported. To provide a more accurate and complete example for users, the necessary import statement has been added.

This change ensures that users who reference this example will have a fully functional code snippet that includes the necessary import for the BashOperator. This will help prevent confusion and potential errors when users attempt to implement the example in their projects.

[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.