Newer pod (hello rawhide) complains if you attempt to mix bullets
and non-bullets in the same list:

virsh.pod around line 3177: Expected text after =item, not a bullet

As our intent was to nest an inner list, we make that explicit to
keep pod happy.

* tools/virsh.pod (ENVIRONMENT): Use correct pod syntax.

(cherry picked from commit 00d69b4a)