Add doctest for circular queue overflow condition

[Tejasrahane]

Added a doctest to test the QUEUE IS FULL exception when attempting to enqueue an element into a full circular queue. This improves test coverage for line 67 in data_structures/queues/circular_queue.py.

Related to #9943

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• 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.
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