Just tried to install 2.3.1 and it looks like the sapphire/dev/install/config-form.html is missing some php start tags. I made the following fixes and it works
now
line 62 & 63
<li>........checked="checked"<?}?> ><label for="EmptyTemplate">..........</li>
becomes:
<li>........checked="checked"<?php } ?> ><label for="EmptyTemplate">..........</li>