(bugfix) (v3.5.1) fix permissions of projects.list file

update-gitweb-access-list had a change recently (289b19d) that had a
side-effect of making projects.list unreadable by other userids (like
'apache' or whatever).

This makes 3.5 unusable for anyone using gitweb.  (Hence the new tag,
too, though 3.5 is only the previous commit and this is a very small
change).