Remove support for Python 3.8

Summary

Removed support for Python 3.8 and removed 3.8 tests from pipeline
https://gitlab.indiscale.com/caosdb/customers/f-fit/management/-/issues/106

Test Environment

Does the pipeline run successfully?

Check List for the Author

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• Annotations in code (Gitlab comments)

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?