Update quick_sort.py

[lt77777]

Closes #6095, reduces the chances of O(n^2) by using median as first pivot rather than end.

Describe your change:

• [ ] Add an algorithm?
• [x] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• [x] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[cclauss]

In preparation for that denial-of-service attack that is Hacktoberfest, I am closing all pull requests that have failing tests.