[ci skip] Add missing NEWS entry

Author: cmb69

NEWS

@@ -21,6 +21,8 @@ PHP                                                                        NEWS
   . mb_detect_encoding recognizes all letters in Czech alphabet (alexdowad)
   . mb_detect_encoding recognizes all letters in Hungarian alphabet (alexdowad)
   . Fixed bug GH-8685 (pcre not ready at mbstring startup). (Remi)
+  . Backwards-compatible mappings for 0x5C/0x7E in Shift-JIS are restored,
+    after they had been changed in 8.1.0. (Alex Dowad)
 
 - OPcache:
   . Fixed bug GH-8591 (tracing JIT crash after private instance method change).