`plot.model_diagnostics()` gives a warning for using deprecated `aes_string()` with ggplot2 >=3.0.0

Reprex:

  library(DALEX)

  # Example from Explanatory Model Analysis, 19 Residual-diagnostics Plots, 19.4 Example: apartment-prices data
  # https://ema.drwhy.ai

  # Make randomForest model
  library("randomForest")
  set.seed(72)

  model_apart_rf <- randomForest(m2.price ~ ., data = apartments)

  explain_apart_rf <- DALEX::explain(
    model = model_apart_rf,
    verbose = F,
    data = apartments_test[, -1],
    y = apartments_test$m2.price,
    label = "Random Forest"
  )

  diag_rf <- model_diagnostics(explain_apart_rf)

  # Figure 19.7: Residuals and predicted values of the dependent variable for the random forest model apartments_rf for the apartments_test dataset.
  plot(diag_rf)

Reproduce the warning with the supplied R example, starting at the plot(diag_rf) entry point for model_diagnostics. Locate the plotting code that emits the deprecated aes_string() warning and verify the completed change by rerunning the example without that warning.