ci: switch to custom python-pypi image

.drone.yml

@@ -5,14 +5,12 @@ name: build and publish
 
 steps:
 - name: build
-  image: python
+  image: registry.kucharczyk.tech/python-pypi
   commands:
-  - python -m pip install build
   - python -m build
 - name: publish
-  image: python
+  image: registry.kucharczyk.tech/python-pypi
   commands:
-  - python -m pip install twine
   - python -m twine upload -u $USERNAME -p $PASSWORD dist/*
   environment:
     USERNAME: