Fix mock handler on Mautic 4

[dennisameling]

NOTE: we probably need a mautic-4 branch and make that the default 😊 CC @RCheesley

bin/console mautic:integrations:sync helloworld results in the following error on Mautic 4:

$ bin/console mautic:integrations:sync helloworld

PHP Fatal error:  Declaration of MauticPlugin\HelloWorldBundle\Connection\MockedHandler::__invoke(Psr\Http\Message\RequestInterface $request, array $options) must be compatible with GuzzleHttp\Handler\MockHandler::__invoke(Psr\Http\Message\RequestInterface $request, array $options): GuzzleHttp\Promise\PromiseInterface in /var/www/html/plugins/HelloWorldBundle/Connection/MockedHandler.php on line 14

Fatal error: Declaration of MauticPlugin\HelloWorldBundle\Connection\MockedHandler::__invoke(Psr\Http\Message\RequestInterface $request, array $options) must be compatible with GuzzleHttp\Handler\MockHandler::__invoke(Psr\Http\Message\RequestInterface $request, array $options): GuzzleHttp\Promise\PromiseInterface in /var/www/html/plugins/HelloWorldBundle/Connection/MockedHandler.php on line 14

This PR fixes that!

Steps to reproduce:

• Install Mautic from GitHub gh repo clone mautic/mautic, make sure you're on the features branch (which is Symfony 4)
• Run cd plugins && gh repo clone mautic/plugin-helloworld HelloWorldBundle
• Clear the cache: rm -rf ../var/cache
• Run bin/console mautic:integrations:sync helloworld, you'll run into the error mentioned above

[RCheesley]

@dennisameling can you push the branch and I will then make it default and apply the branch protection rules! Guessing we should remove the 2 branch? Or keep it for posterity?!

[dennisameling]

@RCheesley sure thing, here it is: https://github.com/mautic/plugin-helloworld/tree/mautic-4 - let's remove the 2 branch indeed!

[RCheesley]

Done!

[kuzmany]

Works for me 👍

[RCheesley]

Just tried to reproduce this in Mautic 4 (features branch) PHP 7.4 and am not able to get the error you mentioned after installing the plugin at command line and then running the command - tried it a few times - have not applied this PR.

ruth.cheesley@MacBookPro-RuthCheesley plugins % ddev exec bin/console mautic:integrations:sync helloworld
[OK] Execution time: 20.785
ruth.cheesley@MacBookPro-RuthCheesley plugins % ddev exec bin/console mautic:integrations:sync helloworld
[OK] Execution time: 1.635
ruth.cheesley@MacBookPro-RuthCheesley plugins % ddev exec bin/console mautic:integrations:sync helloworld
[OK] Execution time: 1.451
ruth.cheesley@MacBookPro-RuthCheesley plugins % ddev exec bin/console mautic:integrations:sync helloworld
[OK] Execution time: 14.398

Totally possible that I missed a step someplace!