[CI] Run black formatter in diff mode before flake8

.gitlab-ci.yml

@@ -31,7 +31,7 @@ test:
 lint:
   stage: test
   script:
-    - tox -e lint,security
+    - tox -e black,lint,security
   allow_failure: true
 
 build_dist:

tox.ini

@@ -33,8 +33,8 @@ commands = poetry build
 [testenv:docs]
 commands = poetry run make -C docs/ html {posargs}
 
-[testenv:autoformat]
-commands = poetry run black {posargs} biscuit/core/
+[testenv:black]
+commands = poetry run black --check --diff biscuit/core/
 
 [flake8]
 max_line_length = 100