I encountered this error as well in moving from 3.0 to the latest 3.3. This was the only thread I could find on the issue and I noticed there was not a concrete solution posted, so I figured it was worth it to bump up a [fairly] old thread to share what worked for me.
In config.php, in the Database Setup section, there is a collation setting that reads thus (emphasis added):
'dbcollation' => 'utf8mb4_unicode_ci', // MySQL has partial and full UTF-8
// support. If you wish to use partial UTF-8
// (three bytes) then set this option to
// 'utf8_unicode_ci', otherwise this option
// can be removed for MySQL (by default it will
// use 'utf8mb4_unicode_ci'. This option should
// be removed for all other databases.
I removed this and my MSSQL database proceeded through the update with no issues.