Faker::Alphanumeric.alphanumeric determinism fix

[admtnnr]

Motivation / Background

This Pull Request has been created because the Faker::Alphanumeric.alphanumeric generator is not deterministic when using min_alpha and/or min_numeric.

Additional information

The generator is not currently deterministic when setting a custom Faker::Config.random due to the usage of the standard shuffle array method.

Unfortunately, this can't be caught by the tests in test/test_determinism.rb because the default keyword arguments do not trigger the non-determinism due to the early return when both min_alpha and min_numeric are 0.

I have added a test to the Faker::Alphanumeric test file for this case, but I'm happy to [re]move it if preferred.

Checklist

Before submitting the PR make sure the following are checked:

• [x] This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• [x] Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• [x] Tests are added or updated if you fix a bug, refactor something, or add a feature.
• [x] Tests and Rubocop are passing before submitting your proposed changes.

If you're proposing a new generator or locale:

• [x] Double-check the existing generators documentation to make sure the new generator you want to add doesn't already exist.
• [x] You've reviewed and followed the Contributing guidelines.