Don't worry - that's final 5.2, not final 5 and, anyway, it's only PHP 4 that is being phased out.
What is happening with PHP 5 is that some bigger enhancements will be merged into a planned PHP 5.3 release. This means the release candidates of PHP 5.2.4 - the final 5.2 patch - need solid testing before being finalized, as you could be using it for a while.
Even if you are still using PHP 4, or PHP 5.1, any testing you do on 5.2.4 right now will benefit you when you get around to upgrading.
PHP 5.2.4 includes OCI8 (and PDO_OCI) of course, as the code base is picked up from PHP's CVS system. Antony is also ready to take a snapshot of OCI8 from CVS for a new PECL OCI8 bundle. So by testing OCI8 in PHP 5.2.4 you are testing what will be in the PECL OCI8 1.2.4 bundle. We've had a few PHP 5 releases since PECL OCI8 1.2.3 was built at the end of Janurary 2007, and various bug fixes have been merged to CVS during that time. Here is the current list of changes that will be in PECL OCI8 1.2.4: