Chore: fix counting of files in performance test

[mdjermanovic]

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What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
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[x] Other, please explain:

Fixes counting of files in the multi-files performance test.

The test works good, it lints 450 files, but the message shows zero.

Multi Files (0 files):

What changes did you make? (Give an overview)

• Path is relative, so it shouldn't slice off C: on Windows (I guess that was the intention).
• The pattern is prepared with quotes, and that's good for a command-line argument, but those quotes should be removed for glob.sync().

Is there anything you'd like reviewers to focus on?