Bump parallel_tests from 2.26.0 to 2.26.2 in /Library/Homebrew/test

Bumps [parallel_tests](https://github.com/grosser/parallel_tests) from 2.26.0 to 2.26.2.
- [Release notes](https://github.com/grosser/parallel_tests/releases)
- [Commits](https://github.com/grosser/parallel_tests/compare/v2.26.0...v2.26.2

)

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