fix: skip edit of files owned by system packages

Skipping the Git system configuration on Whonix weakens the state as it
starts depending on the dotfiles, but it is the only way to not break
system updates due to Whonix security-misc package owning the same file.

Fix: #101

salt/sys-git/install-client.sls

@@ -50,7 +50,15 @@ include:
       - user
       - group
 
+{% if not salt['file.file_exists']('/usr/share/whonix/marker') -%}
+{#
+  Whonix's security-misc package owns /etc/gitconfig, fallback to Git dotfiles
+  to set this option.
+#}
+
 "{{ slsdotpath }}-install-client-allow-protocol":
   cmd.run:
     - name: git config --system protocol.qrexec.allow always
     - runas: root
+
+{% endif -%}