Bump coverage from 7.6.3 to 7.6.4 in /requirements

Bumps [coverage](https://github.com/nedbat/coveragepy) from 7.6.3 to 7.6.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.3...7.6.4)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

requirements/dev-requirements.txt

@@ -2,7 +2,7 @@
 coverage==6.2; python_version<'3.7'
 coverage==7.2.7; python_version>='3.7' and python_version<'3.8'
 coverage==7.6.1; python_version>='3.8' and python_version<'3.9'
-coverage==7.6.3; python_version>='3.9'
+coverage==7.6.4; python_version>='3.9'
 # checks
 flake8==7.1.1
 mypy==1.11.2