Fix postgres hook import pipeline tutorial

[KevinYanesG]

related: #21457

Following @potiuk and @ashb comments I just quickly corrected the PostgresHook imports of the pipeline tutorial.

[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[potiuk]

Merged and cherry-picked to 2.2.4. Thanks @KevinYanesG !