imageavif: Fix default quality (fix #1764)

Author: vrana

reference/image/functions/imageavif.xml

@@ -38,7 +38,7 @@
       <para>
        <parameter>quality</parameter> is optional, and ranges from 0 (worst quality, smaller file)
        to 100 (best quality, larger file).
-       If <literal>-1</literal> is provided, the default value <literal>30</literal> is used.
+       If <literal>-1</literal> is provided, the default value <literal>52</literal> is used.
       </para>
      </listitem>
     </varlistentry>