The container image was still built on Alpine 3.21, which no longer
receives new Python builds: python:3.13-alpine3.21 was last updated in
December 2025. Move the base image to Alpine 3.24, the current Alpine
release.

There is no python:3.13.3-alpine3.24 tag, so PYTHON_VERSION moves from
3.13.3 to 3.13.16, the latest 3.13 patch release published for Alpine
3.24. The Python minor version stays at 3.13.

All packages installed with apk are available in Alpine 3.24;
openssh-client and procps are still resolved through the packages that
provide them (openssh-client-default and procps-ng).

Renovate never proposed an update for the base image. The dockerfile
manager detects registry.osism.tech/dockerhub/python, but the Harbor
proxy cache behind it returns an empty tag list, so the lookup finds
nothing newer. Add a custom regex manager that reads PYTHON_VERSION and
ALPINE_VERSION as one python:<version>-alpine<version> tag, looks it
up on Docker Hub and writes both lines back. Regex versioning treats
the Alpine version as part of the version instead of a fixed suffix,
so Alpine releases are picked up as well. The dockerfile manager entry
for the image is disabled, and separateMinorPatch keeps Python patch
and Alpine updates apart from Python minor updates so they are not
held back by an unmerged minor bump.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Christian Berendt <berendt@osism.tech>