upgrading from 3.1.6 to 3.2.0-a1 with the auto update package at https://download.phpbb.com/pub/release/3.2/unstable/3.2.0-a1/phpBB-3.1.6_to_3.2.0-a1.zip isn't possible.
After merging the update package into the test 3.1.6, and going to url http://localhost:8082/phpbb316/install/, i get a 403 forbidden. there is no index.php in the install folder. so that smoke test failed.
Forbidden

You don't have permission to access /phpbb316/install/ on this server.