Run Tutorials tests less often

[edoaltamura]

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What should we add?

CI tests for tutorials take up most of the runtime (~30 min for each Python version), and updates that affect them are rare. So, the workflow that controls tutorial tests could be modified to run tests only weekly. We could also allow the option to perform these tests on demand if a PR addresses tutorials specifically.

This change would cut the CI runtime for tests not involving tutorials.