Bug fix in OPFDataset parsing (#9623)

In the split of train, test and val, some numbers are hard-coded. This
had to be changed due to introduction of ``num_groups`` that limits the
number of samples that are downloaded.

I completely missed this and forgot to commit this change into the PR.

torch_geometric/datasets/opf.py

@@ -205,9 +205,11 @@ def process(self) -> None:
                     data = self.pre_transform(data)
 
                 i = int(name.split('.')[0].split('_')[1])
-                if i < 270_000:
+                train_limit = int(15_000 * self.num_groups * 0.9)
+                val_limit = train_limit + int(15_000 * self.num_groups * 0.05)
+                if i < train_limit:
                     train_data_list.append(data)
-                elif i < 285_000:
+                elif i < val_limit:
                     val_data_list.append(data)
                 else:
                     test_data_list.append(data)