replace ERR_NUM_ERRORS with PHP_OPENSSL_ERR_BUFFER_SIZE

[jordikroon]

The latest version of OpenSSL removed ERR_NUM_ERRORS from the public API thus we cannot rely on it anymore.

Fixes #21382

[iluuu1994]

Disclosure: I don't know OpenSSL well.

Looks like php_openssl_errors is modeled after ERR_STATE, which became opaque, thus hiding ERR_NUM_ERRORS. I looked at how OPENSSL_G(errors) is used and there don't seem to be any cases where diverging buffer sizes would be problematic.

[bukka]

This looks fine. We might consider targeting lower branches depending how much we will need to change for OpenSSL 4 (meaning if we support it on stable branches). I guess it is fine for master for now and we can backport later...

[remicollet]

@bukka I think it is time to apply in 8.3+

(OpenSSL 4.0 coming to Fedora, and build fails because of this)

For memory, https://copr.fedorainfracloud.org/coprs/yselkowitz/openssl-4.0/monitor/ (test build of all Fedora packages)
See [Build log]https://download.copr.fedorainfracloud.org/results/yselkowitz/openssl-4.0/fedora-rawhide-x86_64/10333654-php/builder-live.log.gz
Also a few set of [-Wdiscarded-qualifiers]