Add python 3.14 release candidate to advancedtools pipeline

Summary

Added a test stage with a python 3.14-rc image to the pipeline.
Part of caosdb-pylib#216 (closed)

Check List for the Author

• All automated tests pass
• Reference related issues
• 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?