fix: fix incorrect error return in ExportAppStateAndValidators

[mdqst]

I fixed an issue in the ExportAppStateAndValidators function where the err variable was incorrectly returned. The variable is already handled inside the function and should not be returned. Instead of returning err in the following line:

}, err

I replaced it with nil to ensure that when there is no error, we return the correct type (error), which should be nil in this case.