Warning when used with Imagick module

Problem/Motivation/Steps to reproduce

When using WebP together with the Imagick module, the warning "Argument 'format' expected by plugin 'imagick_convert' but not passed" is logged when an image is converted to Webp

Proposed resolution

Unlike the ImageMagick module, the Imagick module expects the destination format to be passed as an argument. (It uses this to check with the ImageMagick install whether the format is supported.) We should pass this argument if the Imagick module specifically is the toolkit used.