Add conditional drop_vars execution

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes Notebook output error in CI #585
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Adds a conditional drop_vars call so that legacy environments continue to function

Does this PR introduce a breaking change?

No.

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[Zeitsperre]

PVI @fmigneault

[tlogan2000]

@Zeitsperre possiblly use drop_vars(errors='ignore') ? I'm not sure which is better really. Yours is more explicit i guess