Bump black from 24.3.0 to 26.3.1 in /flowdb/tests

Bumps [black](https://github.com/psf/black) from 24.3.0 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@24.3.0...26.3.1)

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

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

Author: dependabot[bot]

flowdb/tests/Pipfile

@@ -14,7 +14,7 @@ pandas = "*"
 tohu = {file = "https://github.com/maxalbert/tohu/archive/v0.5.1.tar.gz"}
 "psycopg2-binary" = "*"
 descartes = "*"
-black = {extras = ["jupyter"],version = "==24.3.0"}
+black = {extras = ["jupyter"],version = "==26.3.1"}
 
 [requires]
 python_version = "3.11"