Update dependency pytest-cov to v3

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
pytest-cov	>= 2.5.1, <3 -> >=3, <4

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Release Notes

pytest-dev/pytest-cov

v3.0.0

Compare Source

Note that this release drops support for Python 2.7 and Python 3.5.

• Added support for Python 3.10 and updated various test dependencies.
  Contributed by Hugo van Kemenade in
  #&#8203;500 <https://github.com/pytest-dev/pytest-cov/pull/500>_.
• Switched from Travis CI to GitHub Actions. Contributed by Hugo van Kemenade in
  #&#8203;494 <https://github.com/pytest-dev/pytest-cov/pull/494>_ and
  #&#8203;495 <https://github.com/pytest-dev/pytest-cov/pull/495>_.
• Add a --cov-reset CLI option.
  Contributed by Danilo Šegan in
  #&#8203;459 <https://github.com/pytest-dev/pytest-cov/pull/459>_.
• Improved validation of --cov-fail-under CLI option.
  Contributed by ... Ronny Pfannschmidt's desire for skark in
  #&#8203;480 <https://github.com/pytest-dev/pytest-cov/pull/480>_.
• Dropped Python 2.7 support.
  Contributed by Thomas Grainger in
  #&#8203;488 <https://github.com/pytest-dev/pytest-cov/pull/488>_.
• Updated trove classifiers. Contributed by Michał Bielawski in
  #&#8203;481 <https://github.com/pytest-dev/pytest-cov/pull/481>_.
• Reverted change for toml requirement.
  Contributed by Thomas Grainger in
  #&#8203;477 <https://github.com/pytest-dev/pytest-cov/pull/477>_.

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