Handle case where paid plugin update is put into no_update array

[mrsdizzie]

To avoid warning in some cases:

PHP Notice:  Undefined property: stdClass::$requires in /usr/local/etc/wp-cli/packages/vendor/wp-cli/extension-command/src/Plugin_Command.php on line 875

Previously it was assumed the only way an update can be placed into no_update at the server level was if wp.org detected an incompatible WordPress version. Now that it has been released, I've seen that paid plugins which have an updated version the user isn't entitled to can also cause newer versions to end up in the no_update section as well.

Of course it doesn't actually provide a reason anywhere. An example I saw of a paid plugin update that is held back:

object(stdClass)#3821 (6) {
  ["plugin"]=>
  string(29) "gravityformspaypal/paypal.php"
  ["url"]=>
  string(27) "http://www.gravityforms.com"
  ["slug"]=>
  string(18) "gravityformspaypal"
  ["package"]=>
  string(0) ""
  ["new_version"]=>
  string(3) "3.5"
  ["id"]=>
  string(1) "0"
}

And FWIW here is what the above looked like in the WordPress dashboard:

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/Plugin_Command.php	80.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!