[skip ci] UPGRADING.INTERNALS

Author: TimWolla

Diff for: UPGRADING.INTERNALS

@@ -23,6 +23,8 @@ PHP 8.5 INTERNALS UPGRADE NOTES
     for fake closures.
   . Added smart_string_append_printf() matching smart_str_append_printf() for
     char* instead of zend_string*-based smart strings.
+  . Added php_build_provider() to retrieve the value of PHP_BUILD_PROVIDER at
+    runtime.
 
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 2. Build system changes