Fix CAPTCHAs on LimeSurvey

Originally created by @sajolida on #14860 (Redmine)

While creating the dummy survey for Icinga (tails/sysadmin#14859) I realized that we’re probably missing PHP libraries if some day we want to use CAPTCHA.

I configured the dummy survey to require a CAPTCHA before opening before I wanted to prevent filling up our database with spam.

See https://survey.tails.boum.org/index.php/372383?lang=en.

I would try installing php-imagick.

Related issues

• Blocks tails/tails#15392