Plugin method should accept string variable as argument

[neilime]

Fix error "Internal error: Argument passed to Laminas\View\Renderer\PhpRenderer::plugin should be a string, string given" when ViewModel->plugin is called with a variable containing a string instead of a pure string:

$name = 'form';

// ...

$this->getView()->plugin($name);

[Slamdunk]

Hi, thank you for reporting the issue. Can you add tests to your patch please?

[neilime]

@Slamdunk I have added some tests

[Slamdunk]

Thank you @neilime and @ondrejmirtes