fix: git safe repo directory for docker image

Fixes an issue introduced with a recent git update
(https://github.blog/2022-04-12-git-security-vulnerability-announced/)
with a common workaround (actions/checkout#762,
https://stackoverflow.com/questions/71901632/fatal-error-unsafe-repository-home-repon-is-owned-by-someone-else,
actions/checkout#760),
by marking the /data directory inside the container as safe for git
during the container build.

.github/actions/alpine-pandoc-hugo/Dockerfile

@@ -7,4 +7,6 @@ RUN apk --no-cache add ruby git
 COPY delete-script.rb /opt/delete-script.rb
 RUN chmod +x /opt/delete-script.rb
 
+RUN git config --global --add safe.directory /data
+
 ENTRYPOINT ["sh", "-c"]