validate_solutions.py: os.getenv('GITHUB_TOKEN', '')

[cclauss]

@tianyizheng02

Describe your change:

• 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".

[tianyizheng02]

@cclauss From the most recent build in #10542:

    if filepaths := added_solution_file_path():
scripts/validate_solutions.py:62: in added_solution_file_path
    filepath = pathlib.Path.cwd().joinpath(file["filename"])
E   TypeError: string indices must be integers, not 'str'
        file       = 'message'
        files      = {'documentation_url': 'https://docs.github.com/rest', 'message': 'Bad credentials'}
        headers    = {'Accept': 'application/vnd.github.v3+json', 'Authorization': 'token '}
        solution_file_paths = []
...
=========================== short test summary info ============================
ERROR scripts/validate_solutions.py - TypeError: string indices must be integers, not 'str'
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
========================= 1 warning, 1 error in 18.09s =========================
Error: Process completed with exit code 2.