Update UPGRADING.INTERNALS for _zend_hash_find_known_hash

Also add serializable changes, which were missing

Author: morrisonlevi

UPGRADING.INTERNALS

@@ -6,6 +6,8 @@ PHP 8.1 INTERNALS UPGRADE NOTES
   c. zend_get_opcode_id()
   d. Removed support for "p" printf format specifier
   e. ZEND_ATOL() changes
+  f. Non-serializable classes should use ZEND_ACC_NOT_SERIALIZABLE
+  g. _zend_hash_find_known_hash renamed to zend_hash_find_known_hash
 
 2. Build system changes
   a. New compiler flags
@@ -51,6 +53,7 @@ PHP 8.1 INTERNALS UPGRADE NOTES
      ZEND_ACC_NOT_SERIALIZABLE (@not-serializable in stubs) rather than the
      zend_class_(un)serialize_deny handlers. Support for the serialization
      handlers will be dropped in the future.
+  g. _zend_hash_find_known_hash has been renamed to zend_hash_find_known_hash.
 
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 2. Build system changes