NEWS/UPGRADING: fix missing __ in __toString()

Forgotten by yours truly in 36ae82b

[skip ci]

Author: DanielEScherzer

NEWS

@@ -301,7 +301,7 @@ PHP                                                                        NEWS
     (DanielEScherzer)
   . Fixed bug GH-12856 (ReflectionClass::getStaticPropertyValue() returns UNDEF
     zval for uninitialized typed properties). (nielsdos)
-  . Fixed bug GH-15766 (ReflectionClass::toString() should have better output
+  . Fixed bug GH-15766 (ReflectionClass::__toString() should have better output
     for enums). (DanielEScherzer)
   . Added ReflectionProperty::getMangledName() method. (alexandre-daubois)
 

UPGRADING

@@ -391,7 +391,7 @@ PHP 8.5 UPGRADE NOTES
     argument are lower than -1 or if soft_limit is greater than hard_limit.
 
 - Reflection:
-  . The output of ReflectionClass::toString() for enums has changed to
+  . The output of ReflectionClass::__toString() for enums has changed to
     better indicate that the class is an enum, and that the enum cases
     are enum cases rather than normal class constants.
   . The output of ReflectionProperty::__toString() for properties with