Force python symlink creation in test image

Newer Alpine images already ship /usr/bin/python with python3, so a
plain ln -s fails the docker build with 'File exists'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: maennchen

test/Dockerfile

@@ -8,7 +8,7 @@ ENV LANG=C.UTF-8 TERM=xterm
 RUN apk upgrade --update musl && \
     apk add --no-cache autoconf automake bash bc build-base cmake curl git libtool make openssl python3 rsync unzip && \
     rm -rf /var/cache/apk/* && \
-    ln -s /usr/bin/python3 /usr/bin/python
+    ln -sf /usr/bin/python3 /usr/bin/python
 
 RUN mkdir /build
 WORKDIR /build