Pretty strange, since column mentioned is already of type TEXT. Full error message:
[debug_info] => ALTER TABLE `civicrm_logs`.log_civicrm_value_grants_external_application_45 MODIFY `project_outline_673` varchar(4000) COLLATE utf8_unicode_ci DEFAULT NULL [nativecode=1118 ** Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. You have to change some columns to TEXT or BLOBs]
Appears after each security update right at drush cc step. No visible harm (excluding, may be, Change Log records at Contact Tab, which are in a very base format now,mean only name and date, no further details, but not sure if it's relevant).