Adds continuum marker to pytest and continuum tests

[andrewfullard]

Also applies to tests action, splitting it by marker.

📝 Description

Type: 🚦 testing

We are moving back to global vars for our configuration so we need to isolate continuum tests. This achieve it with a custom pytest marker.

🚦 Testing

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☑️ Checklist

• I requested two reviewers for this pull request
• I updated the documentation according to my changes
• I built the documentation by applying the build_docs label

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