PHPC-1922 Update PHONGO_CE_DISABLE_SERIALIZATION for PHP 8.1

[remicollet]

From UPGRADING.INTERNALS

 f. Non-serializable classes should be indicated using the
     ZEND_ACC_NOT_SERIALIZABLE (@not-serializable in stubs) rather than the
     zend_class_(un)serialize_deny handlers which are removed.

[remicollet]

Looks like 8.1 failure is related to outdated version available (some alpha) as the change is for 8.1.0beta1

[alcaeus]

@remicollet thanks for the patch. I'll take a look after the weekend and see where I need to kick the build to fix it

[jmikola]

Note: this may be related to PHPC-1849, although that pertains to the Serializable interface. We may want a new ticket for this PR, which can be added to the same epic for 8.1 support.

[alcaeus]

Verified locally on PHP 8.1, we'll figure out the 8.1 build environment when we pick up PHPC-1850. I've also created PHPC-1922 to track this.

[alcaeus]

Thanks @remicollet!