[renovate] Update python Docker tag to v3.12.0

See merge request !582

Co-authored-by: Renovate Bot <renovate@danet.fbi.h-da.de>

.gitlab/ci/.mk-docs-deploy.yml

 build-mkdocs:
-    image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/python:3.11.5-slim-bookworm
+    image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/python:3.12.0-slim-bookworm
     stage: build
     before_script:
         - pip install mkdocs-material
@@ -13,7 +13,7 @@ build-mkdocs:
         - if: $CI_COMMIT_REF_PROTECTED == "true"
 
 .pages-options: &pages-options
-    image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/python:3.11.5-slim-bookworm
+    image: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/python:3.12.0-slim-bookworm
     stage: deploy
     script:
         - mv mkdocs-built public