TST: clean warnings

[jklenzing]

Description

Updates test flags for the warnings raised when clean is not implemented in preaparation for pysat/pysat#1129

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

with the pysat branch for pysat/pysat#1129

Test Configuration:

• Operating system: Monterrey
• Version number: Python 3.9.7

Checklist:

• Make sure you are merging into the develop (not main) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes
• Update zenodo.json file for new code contributors

If this is a release PR, replace the first item of the above checklist with the release
checklist on the wiki: https://github.com/pysat/pysat/wiki/Checklist-for-Release

[jklenzing]

Not every instrument has discrete cleaning levels. The standard routine is identical for the three levels. Out of scope here, documented in #195. This branch catches existing warnings.