Safari bots have different version of Safari. For example this one has Safari12:
https://logs.chromium.org/logs/flutter/led/nurhan_google.com/5ba142ce8ddb0bb993e02fc3e87a4d1f59fef6ed24566442012512cf1b7106ab/+/steps/all_apps/0/stdout

This one runs 13.0.5: https://logs.chromium.org/logs/flutter/led/nurhan_google.com/51615689552253542b4f41b4619f630a5f44a93566811e888dbc261f38c518c0/+/steps/all_apps/0/stdout

Can we update all the Safari browsers to same version?

(note: Since 12 and 13 versions are drastically different on a few cases, I suspect this might also be the reasons of web unit tests are being flaky time to time.)