Bump black from 25.1.0 to 26.3.1 in /requirements

Bumps [black](https://github.com/psf/black) from 25.1.0 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@25.1.0...26.3.1)

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

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

Author: dependabot[bot]

requirements/requirements_test.txt

@@ -1,4 +1,4 @@
-black==25.1.0
+black==26.3.1
 click>=8.0.2
 isort[requirements]>5.1.0,<=6.0.1
 parameterized