Add upgrading note for crypt change

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Author: nikic

UPGRADING

@@ -457,6 +457,8 @@ PHP 8.0 UPGRADE NOTES
   . Removed deprecated DES fallback in crypt(). If an unknown salt format is
     passed to crypt(), the function will fail with *0 instead of falling back
     to a weak DES hash now.
+  . Specifying out of range rounds for sha256/sha526 crypt() will now fail with
+    *0 instead of clamping to the closest limit. This matches glibc behavior.
   . The result of sorting functions may have changed, if the array contains
     equal-comparing elements.
   . Sort comparison functions return true/false will now throw a deprecation