I found the reason I am getting this error in Rancher trying to edit the GitRepo.
"This is because the GitRepo object's status fields are updated every time Git is polled (by default once every 60 seconds), those changes count as a change to the GitRepo object, and the UI won't let you save changes to an object if someone else has already saved their own changes since you initially loaded it.
So you either have to make you changes quickly, or quickly get in and change the
pollingInterval
for your GitRepo to something longer than 60 seconds."
This is from this Github issue:
https://github.com/rancher/fleet/issues/454