Bump pytest from 6.1.2 to 7.4.0

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.1.2 to 7.4.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@6.1.2...7.4.0)

---
updated-dependencies:
- dependency-name: pytest
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements_dev.txt

@@ -6,7 +6,7 @@ black ==20.8b1
 flake8 >=3.7.7,<4.0
 flake8-import-order >=0.18.1,<0.19
 
-pytest ==6.1.2
+pytest ==7.4.0
 
 # Used in dev.py.
 click >= 7.0,<8.0