add link to php net

Author: raphael-geffroy

reference/configuration/framework.rst

@@ -3895,6 +3895,7 @@ The attributes can also be added to interfaces directly::
 .. _`session.cookie_samesite`: https://www.php.net/manual/en/session.configuration.php#ini.session.cookie-samesite
 .. _`session.cookie_secure`: https://www.php.net/manual/en/session.configuration.php#ini.session.cookie-secure
 .. _`session.gc_divisor`: https://www.php.net/manual/en/session.configuration.php#ini.session.gc-divisor
+.. _`session.gc_probability`: https://www.php.net/manual/en/session.configuration.php#ini.session.gc-probability
 .. _`session.gc_maxlifetime`: https://www.php.net/manual/en/session.configuration.php#ini.session.gc-maxlifetime
 .. _`session.sid_length`: https://www.php.net/manual/en/session.configuration.php#ini.session.sid-length
 .. _`session.sid_bits_per_character`: https://www.php.net/manual/en/session.configuration.php#ini.session.sid-bits-per-character