ci: fix missing dependency for isort

.drone.yml

@@ -8,6 +8,7 @@ steps:
   - name: check style
     image: python:3.12-alpine
     commands:
+      - apk add --no-cache git  # required by isort to skip files in .gitignore
       - pip install black isort
       - black --check .
       - isort -c .