Update importlib-metadata requirement from <6.7 to <6.8

Updates the requirements on [importlib-metadata](https://github.com/python/importlib_metadata) to permit the latest version.
- [Release notes](https://github.com/python/importlib_metadata/releases)
- [Changelog](https://github.com/python/importlib_metadata/blob/main/CHANGES.rst)
- [Commits](python/importlib_metadata@0.1...v6.7.0)

---
updated-dependencies:
- dependency-name: importlib-metadata
  dependency-type: direct:production
...

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

test_reqs.txt

@@ -1,7 +1,7 @@
 django-treebeard==4.7
 Markdown>=2.6.11,<3
 coverage==7.2.7
-importlib-metadata<6.7  # for flake8
+importlib-metadata<6.8  # for flake8
 typing_extensions==4.6.3
 zipp==3.15.0  # for flake8
 flake8==6.0.0