ContextRequireExceptionKeyRule should support `non-capturing catches`

[sasezaki]

Also see refs. phpstan/phpstan#8663 ( Catching exception without capturing on PHP 7.4 is not allowed )
https://wiki.php.net/rfc/non-capturing_catches

Currently, would not be detected by ContextRequireExceptionKeyRule below case.

try {
  print 'Lets do something nasty here.';
  throw new Exception('This is nasty');
} catch (Exception) {
  print 'Exception occured';
  $this->logger->error('error happend'); // should be reported as requires \'exception\' key. 

Because, ContextRequireExceptionKeyRule does detects with findCurrentScopeThrowableVariable.