Fixes bug in PriorityQueue Algorithm; Fixes syntax in code for array.

[Kpraful]

Describe your change:

There was a bug in PriorityQueue class due to which extract_min function was giving wrong output, hence fixed it.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• 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.
• 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".

[praful-katare]

Reviewed the changes, please close the PR.

[cclauss]

It is extremely difficult to review proposed changes to a complex Python file that has no tests.
Would you be willing to open another pull request to add doctests to the functions of the existing algorithm?

See #9943 for a general request for more tests of our algorithms.

[Kpraful]

If I add doctests in the previous algorithm then it will fail, therefore I was first trying to fix the code and then add doctests to it.
What should I do now? Create another PR add doctests and fix the bug in the same PR?

[cclauss]

Make a separate PR that includes a doctest that proves the current code fails. Then it will be much easier to review this pull request. Do NOT add tests AND fixes in the SAME pull request. Tests in one PR and fixes in another PR.