build(deps-dev): bump black from 25.12.0 to 26.3.1

Bumps [black](https://github.com/psf/black) from 25.12.0 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@25.12.0...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]

poetry.lock

@@ -29,7 +29,7 @@ requests = "^2.32.3"
 pytest = "^8.3.5"
 coverage = "^7.13.4"
 flake8 = "^7.2.0"
-black = "^25.1.0"
+black = "^26.3.1"
 pip-licenses = "^5.0.0"
 jinja2 = "^3.1.6"
 pytest-nhsd-apim = "^5.0.0"