Add doctest to trapezoidal_rule

[kyrtsouv]

Describe your change:

Contributes to #9943

• [ ] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [x] Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• [ ] 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.
• [ ] All new Python files are placed inside an existing directory.
• [ ] All filenames are in all lowercase characters with no spaces or dashes.
• [ ] All functions and variable names follow Python naming conventions.
• [ ] All function parameters and return values are annotated with Python type hints.
• [ ] All functions have doctests that pass the automated testing.
• [ ] All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• [ ] If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[kyrtsouv]

What do you mean? Are the doctests wrong or are you talking about the ruff check failing? Because I don't know why it fails I didn't change anything to the directories that it checks.

[tianyizheng02]

@kyrtsouv The doctests seem to be fine since the build passes. The ruff errors are probably due to newly added ruff rules—try rebasing your code to get it up-to-date and see if that fixes things.