fix: make bubble sort work with comparable items

[nikhiltumma]

Fix bubble sort comparisons to use the __lt__ operation defined by the Comparable protocol.

Tests:

• python sorts/bubble_sort.py
• python -m doctest -v sorts/bubble_sort.py

All 42 doctests pass.

Checklist

• I have read the contributing guidelines.
• I have tested my changes locally.
• The modified code runs successfully.
• All existing doctests pass.
• I have checked that my changes follow the repository's coding style.
• I have kept my changes focused on the issue.
• I have not modified the README.md or DIRECTORY.md files.

Fixes #15234

[algorithms-keeper]

Closing this pull request as invalid

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