Add dry-run Docker build to Pull Request CI run

.drone.yml

@@ -15,7 +15,7 @@ trigger:
 
 steps:
   - name: install-lint-test
-    image: python:3.9.20-alpine@sha256:eb37f58646a901dc7727cf448cae36daaefaba79de33b5058dab79aa4c04aefb
+    image: python:3.8.19-alpine@sha256:c2f31d16113f2c1152934d321855c9f0169143dff96d716dada19e0047d6ddee
     env:
       PYROOT: '/pyroot'
       PYTHONUSERBASE: '/pyroot'
@@ -26,6 +26,16 @@ steps:
       - pipenv run flake8
       - pipenv run reuse lint
       - pipenv run python -m unittest discover ki
+  - name: docker-dry-run
+    image: plugins/docker:20.18.4@sha256:a8d3d86853c721492213264815f1d00d3ed13f42f5c1855a02f47fa4d5f1e042
+    settings:
+      registry: git.wtf-eg.de
+      repo: git.wtf-eg.de/kompetenzinventar/backend
+      target: ki-backend
+      dry_run: true
+    when:
+      event:
+        - pull_request
 
 ---
 kind: pipeline
@@ -93,7 +103,7 @@ trigger:
 
 steps:
   - name: install-lint-test
-    image: python:3.9.20-alpine@sha256:eb37f58646a901dc7727cf448cae36daaefaba79de33b5058dab79aa4c04aefb
+    image: python:3.8.19-alpine@sha256:c2f31d16113f2c1152934d321855c9f0169143dff96d716dada19e0047d6ddee
     env:
       PYROOT: '/pyroot'
       PYTHONUSERBASE: '/pyroot'

.python-version

@@ -1 +1 @@
-3.9.20
+3.8.19

Dockerfile

@@ -2,7 +2,7 @@
 #
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-FROM python:3.9.20-alpine@sha256:eb37f58646a901dc7727cf448cae36daaefaba79de33b5058dab79aa4c04aefb AS builder
+FROM python:3.8.19-alpine@sha256:c2f31d16113f2c1152934d321855c9f0169143dff96d716dada19e0047d6ddee AS builder
 
 ENV PYROOT=/pyroot
 ENV PYTHONUSERBASE=$PYROOT
@@ -20,7 +20,7 @@ RUN PIP_USER=1 PIP_IGNORE_INSTALLED=1 pipenv install --system --deploy --ignore-
 RUN pip3 uninstall --yes pipenv
 
 
-FROM python:3.9.20-alpine@sha256:eb37f58646a901dc7727cf448cae36daaefaba79de33b5058dab79aa4c04aefb AS ki-backend
+FROM python:3.8.19-alpine@sha256:c2f31d16113f2c1152934d321855c9f0169143dff96d716dada19e0047d6ddee AS ki-backend
 
 ENV PYROOT=/pyroot
 ENV PYTHONUSERBASE=$PYROOT