Bump black from 25.9.0 to 26.3.1

Bumps [black](https://github.com/psf/black) from 25.9.0 to 26.3.1.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@25.9.0...26.3.1)

---
updated-dependencies:
- dependency-name: black
  dependency-version: 26.3.1
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

pyproject.toml

@@ -44,10 +44,10 @@ dev-flake8 = [
   "pydoclint == 0.7.6",
   "pydocstyle == 6.3.0",
 ]
-dev-formatting = ["black == 25.9.0", "isort == 8.0.1"]
+dev-formatting = ["black == 26.3.1", "isort == 8.0.1"]
 dev-mkdocs = [
   "Markdown == 3.10.2",
-  "black == 25.9.0",
+  "black == 26.3.1",
   "frequenz-repo-config[lib] == 0.17.0",
   "markdown-callouts == 0.4.0",
   "markdown-svgbob == 202406.1023",