add php opcache, some testing for https://github.com/opnsense/core/issues/2320 looks harmless to add to our port selection

Eventually the nightly build should continue and log failures
at the very bottom where they are easiest to review.  For now
start with logging the port build that caused the error and
then we'll work our way up to build continuation.

Seems to be a recently introducted ports build problem.

... even though we don't use it directly anymore.  We may need fixes.

PR: https://github.com/opnsense/core/issues/2357

Historically, opnsense category was built first to ensure
consistency with PHP/Python version, but that is no longer
the case since FreeBSD introduced flavors.