Update dependency parallel_tests to v5.6.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
parallel_tests (changelog)	'= 5.5.0' → '= 5.6.0'

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Release Notes

grosser/parallel_tests (parallel_tests)

v5.6.0

Compare Source

Fixed

• Fixed grammar in duration message to use singular "second" when appropriate (e.g., "Took 1 second" instead of "Took 1 seconds")
• Return correct exit status when process was terminated

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