Fix RSpec/DescribedClass warning

[gavindidrichsen]

Prior to this the following error occurred: RSpec/DescribedClass: Use `described_class` instead of `PuppetLint::Lexer`. (https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/DescribedClass)

Summary

Provide a detailed description of all the changes present in this pull request.

Additional Context

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• [ ] Root cause and the steps to reproduce. (If applicable)
• [ ] Thought process behind the implementation.

Related Issues (if any)

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Checklist

• [ ] 🟢 Spec tests.
• [ ] 🟢 Acceptance tests.
• [ ] Manually verified.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.19%. Comparing base (d0e5560) to head (1dd75e3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #194 +/- ## ======================================= Coverage 93.19% 93.19% ======================================= Files 55 55 Lines 1792 1792 ======================================= Hits 1670 1670 Misses 122 122 ```

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