Bug Font Awesome Icon is not displayed with <xf:fa>

[Kirby]

Prerequisites
Development mode must be disabled

Steps to reproduce
Create an ad for position Container Content: Above with the following content
Code:

<xf:set var="$icon" value="fa-ambulance" />
<xf:fa icon="{$icon|raw}" />

Expected result
The ambulance icon is shown when viewing a public page just like it is in XF 2.2

Actual result
The HTML source code for the page contains
Code:

<i class="fa--xf far fa-ambulance ">
    <svg...

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