Inconsistent directory permissions for ~/.docker directory #2727

Opening as a tracking issue, following the discussion on moby/buildkit#1660 (comment), which highlighted that depending on which path in the code is taken, permissions on the ~/.docker may be either 0700 or 0755;

The second example was added later, so should probably be updated to match the former, although less restrictive permissions would likely not be a problem in most cases as this directory (in the default case) will be inside the user's home directory, which should already be inaccessible for other users.