[php-src] Issue #21617: sni_server self signed certifcate expired

Issue: https://github.com/php/php-src/issues/21617
Author: ptondereau

### Description

Since April 2nd, the self-signed certificate has expired, leading to always failing tests:

```
sni_server [ext/openssl/tests/sni_server.phpt]
sni_server with separate pk and cert [ext/openssl/tests/sni_server_key_cert.phpt]
```

```
openssl x509 -in ext/openssl/tests/sni_server_cs.pem -noout -enddate
notAfter=Apr  2 18:36:12 2026 GMT
```


### PHP Version

```plain
PHP 8.5.2-dev (cli) (built: Jan 27 2026 14:27:04) (NTS DEBUG)
Copyright (c) The PHP Group
Zend Engine v4.5.2-dev, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.2-dev, Copyright (c), by Zend Technologies
```

### Operating System

_No response_