Update NEWS/UPGRADING for ++ on string deprecation

Author: Girgias

NEWS

@@ -21,6 +21,9 @@ PHP                                                                        NEWS
     references). (Arnaud, timwolla)
   . Introduced the TAILCALL VM, enabled by default when compiling with Clang>=19
     on x86_64 or aarch64. (Arnaud)
+  . Enacted the follow-up phase of the "Path to Saner Increment/Decrement
+    operators" RFC, meaning that incrementing non-numeric strings is now
+    deprecated. (Girgias).
 
 - Filter:
   . Added support for configuring the URI parser for FILTER_VALIDATE_URL

UPGRADING

@@ -356,6 +356,10 @@ PHP 8.5 UPGRADE NOTES
   . Constant redeclaration is deprecated and that behavior will trigger an
     error in PHP 9.
     RFC: https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_constant_redeclaration
+  . Enacted the follow-up phase of the "Path to Saner Increment/Decrement
+    operators" RFC, meaning that incrementing non-numeric strings is now
+    deprecated. Instead the str_increment() function should be used.
+    RFC: https://wiki.php.net/rfc/deprecations_php_8_5#enact_follow-up_phase_of_the_path_to_saner_incrementdecrement_operators_rfc
 
 - Curl:
   . The curl_close() function has been deprecated, as CurlHandle objects are