Fix type incompatibility in assignment.

This partially reverts 0956267, which
introduced a type incompatibility where an `int` function is assigned
to a `zend_result` function.  That yields a level 1 C4133 warning on
MSVC, and usually (e.g. in CI) level 1 warnings are elevated to errors,
so the build fails.[1]

The PHP-8.3 branch and up are uneffected by this, so the upward merges
should be empty.

[1] <0956267#r144587696>

Author: cmb69

ext/session/session.c

@@ -56,8 +56,9 @@
 
 PHPAPI ZEND_DECLARE_MODULE_GLOBALS(ps)
 
-static zend_result php_session_rfc1867_callback(unsigned int event, void *event_data, void **extra);
-static zend_result (*php_session_rfc1867_orig_callback)(unsigned int event, void *event_data, void **extra);
+static int php_session_rfc1867_callback(unsigned int event, void *event_data, void **extra);
+/* the following signature must match (*php_rfc1867_callback) in main/rfc1867.h */
+static int (*php_session_rfc1867_orig_callback)(unsigned int event, void *event_data, void **extra);
 static void php_session_track_init(void);
 
 /* SessionHandler class */