[R] fix lintr exclude (#11090)

R-package/R/xgb.train.R

@@ -390,7 +390,7 @@ xgb.train <- function(params = xgb.params(), data, nrounds, evals = list(),
   return(bst)
 }
 
-# nolint start: line_length_linter
+# nolint start: line_length_linter.
 #' @title XGBoost Parameters
 #' @description Convenience function to generate a list of named XGBoost parameters, which
 #' can be passed as argument `params` to [xgb.train()]. See the [online documentation](