Dockerfile: use alpine as base image

- We require bash-5.3, and the debian base image only provides up to
  bash-5.2. Alpine provides bash-5.3, so switch to that.
- It is also smaller, which is a nice bonus.
- Also disabled git safe-directory check, as I don't think any usage
  of this image would involve untrusted repositories, so this is just
  an annoyance.

When we have python docker images based on newer debian with bash-5.3,
we can consider switching back to debian, or even giving users a choice
between debian and alpine based images.

Resolves: pkgcore/pkgcheck-action#21
Signed-off-by: Arthur Zamarin <arthurzam@gentoo.org>

Author: arthurzam

Dockerfile

@@ -1,9 +1,11 @@
-FROM python:3-slim
+FROM python:3-alpine
 ARG PKGCHECK_VERSION
 
-RUN apt-get update && apt-get install -y --no-install-recommends git zstd cpanminus make && \
+RUN apk add --no-cache "bash>=5.3" git perl xz zstd && \
+    apk add --no-cache --virtual .cpanm make perl-app-cpanminus && \
     cpanm --quiet --notest Gentoo::PerlMod::Version && \
-    apt remove --autoremove -y make cpanminus && \
-    rm -rf /var/lib/apt/lists/ /var/cache/apt /var/cache/dpkg && \
-    pip install pkgcheck==${PKGCHECK_VERSION} setuptools requests && \
-    pip cache purge
+    apk del .cpanm make perl-app-cpanminus && \
+    pip install --root-user-action=ignore pkgcheck==${PKGCHECK_VERSION} setuptools requests && \
+    pip cache purge && \
+    ln -sv /bin/bash /usr/bin/bash && \
+    git config --global --add safe.directory '*'