Updating version file to reflect that 12.16 has been branched.

Created by: jwillenbring

Updating to 12.17 for now because in Trilinos 13 we are going to break backward compatibility and don't want to do so quite yet. Also, we are planning to change the versioning approach. This change does not indicate we are planning a 12.18 release.

@trilinos/framework

Description

I am updating the version of Trilinos on the development branch, which will eventually be promoted to the master branch, to make it clear that this is not the development version of Trilinos prior to 12.16.