Set git `safe.directory` in tool containers

Otherwise it hit the "dubious ownership" case.

_test_tools/httpd/Dockerfile

@@ -42,6 +42,8 @@ RUN htpasswd -b -c /etc/htpasswd testuser testpass
 
 # Callers should mount a directory with git repos here.
 VOLUME /git
+# sshd runs as root, and the repo directory might be owned by anyone.
+RUN git config --system safe.directory '*'
 
 COPY nginx.conf /etc/nginx/
 COPY run.sh /

_test_tools/sshd/Dockerfile

@@ -49,6 +49,8 @@ VOLUME /dot_ssh
 
 # Callers should mount a directory with git repos here.
 VOLUME /git
+# sshd runs as root, and the repo directory might be owned by anyone.
+RUN git config --system safe.directory '*'
 
 # Callers can SSH as user "test"
 RUN echo "test:x:65533:65533::/home/test:/usr/bin/git-shell" >> /etc/passwd