Fix reference handling of IntlTimeZone::getCanonicalID/intltz_get_canonical_id

Closes GH-18469.

ext/intl/tests/intltz_get_canonical_id_refs.phpt

@@ -0,0 +1,19 @@
+--TEST--
+IntlTimeZone::getCanonicalID: refs test
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+class Test {
+    public string $prop = "a";
+}
+$test = new Test;
+$ref =& $test->prop;
+print_R(intltz_get_canonical_id('Portugal', $ref));
+var_dump($test);
+?>
+--EXPECT--
+Europe/Lisbonobject(Test)#1 (1) {
+  ["prop"]=>
+  &string(1) "1"
+}

ext/intl/timezone/timezone_methods.cpp

@@ -291,9 +291,7 @@ U_CFUNC PHP_FUNCTION(intltz_get_canonical_id)
 	RETVAL_NEW_STR(u8str);
 
 	if (is_systemid) { /* by-ref argument passed */
-		ZVAL_DEREF(is_systemid);
+		ZEND_TRY_ASSIGN_REF_BOOL(is_systemid, isSystemID);
-		zval_ptr_dtor(is_systemid);
-		ZVAL_BOOL(is_systemid, isSystemID);
 	}
 }