Improve cleanup of tests

[Mati365]

Suggested merge commit message (convention)

Tests: Add react testing library cleanup call before each test to reduce amount of flaky tests. Closes https://github.com/ckeditor/ckeditor5-react/issues/542

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Additional information

It looks like error handling in vitest doesn't play well with CKEditor error handling.

[coveralls]

Pull Request Test Coverage Report for Build c3c4d789-e636-41fe-9523-bbce3022b2a8

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 876c9cb3-a6b3-4602-b29a-c127317e1f8b:	0.0%
Covered Lines:	582
Relevant Lines:	582

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💛 - Coveralls