Crash at end of regression runs

[mszulcz-mitre]

When I make a run with cfg.dataset.task_type = 'regression', the code crashes at the end of the run. The error message is:

Traceback (most recent call last):
 File "main_pyg.py", line 55, in <module>
   agg_runs(cfg.out_dir, cfg.metric_best)
 File "~/Code/GraphGym/graphgym/utils/agg_runs.py", line 100, in agg_runs
   [stats[metric] for stats in stats_list])
 File "~/Code/GraphGym/graphgym/utils/agg_runs.py", line 100, in <listcomp>
   [stats[metric] for stats in stats_list])
KeyError: 'accuracy'

The problem seems to be that accuracy is not a metric logged for regression tasks. Here are the relevant lines in agg_runs.py:

                if metric_best == 'auto':
                    metric = 'auc' if 'auc' in stats_list[0] else 'accuracy'

Here's a fix:

                if metric_best == 'auto':
                    if cfg.dataset.task_type == 'classification':
                        metric = 'auc' if 'auc' in stats_list[0] else 'accuracy'
                    elif cfg.dataset.task_type == 'regression':
                        metric = 'mse'