ext/pcntl: fix declared signature of pcntl_signal($restart_syscalls)

ext/pcntl/pcntl.stub.php

@@ -1023,7 +1023,7 @@ function pcntl_waitid(int $idtype = P_ALL, ?int $id = null, &$info = [], int $fl
     function pcntl_wait(&$status, int $flags = 0, &$resource_usage = []): int {}
 
     /** @param callable|int $handler */
-    function pcntl_signal(int $signal, $handler, bool $restart_syscalls = true): bool {}
+    function pcntl_signal(int $signal, $handler, ?bool $restart_syscalls = null): bool {}
 
     /** @return callable|int */
     function pcntl_signal_get_handler(int $signal) {}

ext/pcntl/tests/pcntl_signal_restart_syscalls.phpt

@@ -0,0 +1,36 @@
+--TEST--
+pcntl_signal(): $restart_syscalls is nullable
+--EXTENSIONS--
+pcntl
+--FILE--
+<?php
+declare(strict_types=1);
+
+$parameter = (new ReflectionFunction('pcntl_signal'))->getParameters()[2];
+var_dump((string) $parameter->getType());
+var_dump($parameter->allowsNull());
+var_dump($parameter->getDefaultValue());
+
+var_dump(pcntl_signal(SIGALRM, SIG_IGN));
+var_dump(pcntl_signal(SIGALRM, SIG_IGN, null));
+var_dump(pcntl_signal(SIGALRM, SIG_IGN, true));
+var_dump(pcntl_signal(SIGALRM, SIG_IGN, false));
+
+try {
+    pcntl_signal(SIGALRM, SIG_IGN, 1);
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+
+var_dump(pcntl_signal(SIGALRM, SIG_DFL));
+?>
+--EXPECT--
+string(5) "?bool"
+bool(true)
+NULL
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+TypeError: pcntl_signal(): Argument #3 ($restart_syscalls) must be of type ?bool, int given
+bool(true)