bump black to 26.3.1

Author: sathiya-nhs

poetry.lock

@@ -30,7 +30,7 @@ requests = "^2.32.3"
 pytest = "^8.3.5"
 coverage = "^7.8.0"
 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"