Update pytest requirement from ==6.2.* to >=6.2,<8.4

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@6.2.0.dev0...8.3.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

setup.py

@@ -25,7 +25,7 @@
       extras_require={
           'test': [
             'pylint==2.8.*',
-            'pytest==6.2.*',
+            'pytest>=6.2,<8.4',
             'pytest-cov==2.12.*',
             'unify==0.5'
           ]