Update dependency pytest-cov to v6

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
pytest-cov (changelog)	>=5,<6 -> >=6,<7

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Release Notes

pytest-dev/pytest-cov (pytest-cov)

v6.0.0

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• Updated various documentation inaccuracies, especially on subprocess handling.
• Changed fail under checks to use the precision set in the coverage configuration.
  Now it will perform the check just like coverage report would.
• Added a --cov-precision cli option that can override the value set in your coverage configuration.
• Dropped support for now EOL Python 3.8.

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