Generic/ForLoopShouldBeWhileLoop: fix E_DEPRECATED error

This commit fixes an issue in the sniff that could result in the following E_DEPRECATED
error when running PHP 8.3:

```
Decrement on type null has no effect, this will change in the next major version of PHP

src/Standards/Generic/Sniffs/CodeAnalysis/ForLoopShouldBeWhileLoopSniff.php:65
```

This sniff relies on finding the position of the open and closing
parentheses for a given `for` loop. However, the problem was that there was
no defensive code for cases when the closing parenthesis is missing. The
sniff would still work when running PHP >= 8.2, but on PHP 8.3 it would
throw the deprecated message above.

This would happen because since there is no closing parenthesis `$end` is set to null,
and $next <= $end always evaluates to false
(https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/84acf4e56f110db8e75cb9a575c5727df637643c/src/Standards/Generic/Sniffs/CodeAnalysis/ForLoopShouldBeWhileLoopSniff.php#L74).

The issue was fixed by bailing early if the closing parenthesis is
missing. A test with a `for` loop without the closing parenthesis was added.

src/Standards/Generic/Sniffs/CodeAnalysis/ForLoopShouldBeWhileLoopSniff.php

@@ -57,7 +57,7 @@ public function process(File $phpcsFile, $stackPtr)
         $token  = $tokens[$stackPtr];
 
         // Skip invalid statement.
-        if (isset($token['parenthesis_opener']) === false) {
+        if (isset($token['parenthesis_opener']) === false || isset($token['parenthesis_closer']) === false) {
             return;
         }
 

src/Standards/Generic/Tests/CodeAnalysis/ForLoopShouldBeWhileLoopUnitTest.3.inc

@@ -0,0 +1,4 @@
+<?php
+
+// Intentional parse error. Testing that the sniff is *not* triggered in this case.
+for ($i = 0; $i < 10; $i++