Update black requirement from <26 to <27

Updates the requirements on [black](https://github.com/psf/black) to permit the latest version.
- [Release notes](https://github.com/psf/black/releases)
- [Changelog](https://github.com/psf/black/blob/main/CHANGES.md)
- [Commits](psf/black@18.3a0...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

@@ -124,7 +124,7 @@ doc = [
 
 # pip requirements for all the CI builds
 test = [
-    "black<26",
+    "black<27",
     "certifi",
     "coverage!=6.3",
     "psutil; sys_platform != 'cygwin'",