refactor: Don't build muliterrors for a single error

For caller convenience multierror.New might be called with only a single
error in a list of errors.
In these cases there is no value of wrapping the error in a multierror
so New simply returns the single error it was called with.

internal/mutlierror/multierror.go

@@ -36,6 +36,10 @@ func (m MultiError) Error() string {
 }
 
 func New(errs ...error) error {
+	if len(errs) == 1 {
+		// callers might not always check this beforehand, but building a MultiError for a single error is useless
+		return errs[0]
+	}
 	return MultiError{
 		Errors: errs,
 	}