fix(error): avoid override errors on rollback

[balanza]

Redeclare err in the rollback() scope so that it does not override the outer scope.

Example

if err != nil {
	rollback()
	return "", fmt.Errorf("start sidecar: %w", err)
}

# before
level=INFO msg="Error: start sidecar: %!w(<nil>)"

# after
level=INFO msg="Error: start sidecar: exit status 126"