Add Ghostscript to persistent package list for ImageMagick

[Teko012]

This pull request makes a small update to the install-php-extensions script to improve dependency handling for ImageMagick extensions.

• Added ghostscript to the list of persistent required packages when installing ImageMagick-related PHP extensions, ensuring better compatibility and support for image processing features.

The Alpine variant already has it, but it's missing on Debian. It is required for PDF handling.

[mlocati]

How big is ghostscript?

[Teko012]

@mlocati On Alpine, which the script already installs, it's 62.9MiB. The one we add for Debian now is 57.5 MB.

[mlocati]

Do you have a small PHP script that can be used to test whether imagick works correctly with PDF files?

[Teko012]

@mlocati I added a script. The test seems to have failed due to some unrelated Docker issue, but the relevant part has passed. Maybe you can rerun the failed ones, they should pass too.

[Teko012]

@mlocati Can we merge this in? It might cause a merge conflict with #1306, which I would need to fix

[mlocati]

You removed testing the case when imagick supports reading a format, but doesn't support writing it (eg when the value is false).
For example, we previously had 'PDF' => false, meaning that imagick was listed in the result of Imagick::queryFormats().

Also, please don't be so verbose in comments.