Update diff-cover requirement from <7.6 to <7.7

Updates the requirements on [diff-cover](https://github.com/Bachmann1234/diff-cover) to permit the latest version.
- [Release notes](https://github.com/Bachmann1234/diff-cover/releases)
- [Changelog](https://github.com/Bachmann1234/diff_cover/blob/main/CHANGELOG)
- [Commits](Bachmann1234/diff_cover@v0.1.0...v7.6.0)

---
updated-dependencies:
- dependency-name: diff-cover
  dependency-type: direct:development
...

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

Author: dependabot[bot]

dev-requirements.txt

@@ -1,4 +1,4 @@
-diff_cover < 7.6
+diff_cover < 7.7
 pylint < 2.18
 pydocstyle < 6.4
 flake8 > 4