Update pytest requirement from <7.0.0,>=5.3.5 to >=5.3.5,<8.0.0 (#591)

Updates the requirements on [pytest](https://github.com/pytest-dev/pytest) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@5.3.5...7.0.0)

---
updated-dependencies:
- dependency-name: pytest
  dependency-type: direct:development
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/dev.txt

@@ -4,7 +4,7 @@ flake8>=3.7.7, <6.0.0
 mypy~= 0.900
 types-requests>=2.25.0, <3.0.0
 # testing
-pytest>=5.3.5, <7.0.0
+pytest>=5.3.5, <8.0.0
 pytest-cov>=2.6.1, <4.0.0
 pytest-xdist>=1.28.0, <3.0.0 # for distributed testing, currently unused (see setup.cfg)
 pytest-lazy-fixture>=0.6.3, <0.7.0