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?

assigned to @i.nueske

marked the checklist item All automated tests pass as completed

marked the checklist item Annotations in code (Gitlab comments) as completed

requested review from @florian

marked the checklist item I understand the intent of this MR as completed

marked the checklist item All automated tests pass as completed

marked the checklist item Up-to-date CHANGELOG.md (or not necessary) as completed

marked the checklist item Appropriate user and developer documentation (or not necessary) as completed

marked the checklist item The test environment setup works and the intended behavior is reproducible in the test as completed

marked the checklist item In-code documentation and comments are up-to-date. as completed

resolved all threads

mentioned in commit 20f39511

merged