build(deps): update pytest-cov requirement from <4,>=3 to >=3,<5 (#21)

Updates the requirements on [pytest-cov](https://github.com/pytest-dev/pytest-cov) to permit the latest version.
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v3.0.0...v4.1.0)

---
updated-dependencies:
- dependency-name: pytest-cov
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements/testing.txt

@@ -1,6 +1,6 @@
 # pip install -r requirements/testing.txt
 pytest>=6.2.5,<7
-pytest-cov>=3,<4
+pytest-cov>=3,<5
 Flask>=2.0.3,<4 
 gevent>=22.10.2,<24
 gevent-websocket>=0.10.1,<1