Fix workflow sample notebook url

[94rain]

Describe your changes

I was following this tutorial to build the docker image with docker build --tag ploomber-workflow . in tutorials/workflow

It failed while downloading a notebook.

Looks like it is due to the migration of these notebooks from the ploomber/soorgeon repo to the ploomber/ci-notebooks repo.

I updated the notebook URL to link to the ci-notebooks repo.

I think we also need CI for building docker images to prevent issues like from happening.

Issue ticket number and link

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Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] I have added thorough tests (when necessary).
• [x] I have added the right documentation (when needed). Product update? If yes, write one line about this update.