Fix a typo in UPGRADING

Author: TysonAndre

UPGRADING

@@ -70,7 +70,7 @@ PHP 8.0 UPGRADE NOTES
     will now always generate a fatal error. Previously a warning was generated
     in some cases.
     RFC: https://wiki.php.net/rfc/lsp_errors
-  . The precendence of the concatenation operator has changed relative to
+  . The precedence of the concatenation operator has changed relative to
     bitshifts and addition as well as subtraction.
     RFC: https://wiki.php.net/rfc/concatenation_precedence