Bump coverage from 7.6.7 to 7.6.8

Bumps [coverage](https://github.com/nedbat/coveragepy) from 7.6.7 to 7.6.8.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.7...7.6.8)

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

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

setup.py

@@ -17,7 +17,7 @@
     packages=find_packages(),
     include_package_data=True,
     install_requires=requirements,
-    extras_require={"test": ["coverage==7.6.7", "pytest==8.3.3", "pytest-cov==6.0.0", "tox==4.23.2"]},
+    extras_require={"test": ["coverage==7.6.8", "pytest==8.3.3", "pytest-cov==6.0.0", "tox==4.23.2"]},
     entry_points="""
         [console_scripts]
         xml-validate=validator.__main__:cli