Character set 'utf8' is not a compiled character set and is not specified in the '/usr/share/mysql/charsets/Index.xml' file

From the change log for 10.6.11 :

The utf8 character set (and related collations) is now by default an alias for utf8mb3 rather than the other way around. It can be set to imply utf8mb4 by changing the value of the old_mode system variable (MDEV-8334)

The alias for charset utf8mb3 is set to utf-8 but the old charset name was utf8 (without -)

From /usr/share/mysql/charsets/Index.xml
<charset name="utf8mb3">
<family>Unicode</family>
<description>UTF-8 Unicode</description>
<alias>utf-8</alias>
<alias>utf8</alias> #missing after the update