[Fix] Update ST_SA_MJ_train.py (#1117)

Fix a bug that results train3's parameter covering the train1 and train2

configs/_base_/recog_datasets/ST_SA_MJ_train.py

@@ -29,14 +29,20 @@ train2 = {key: value for key, value in train1.items()}
 train2['img_prefix'] = train_img_prefix2
 train2['ann_file'] = train_ann_file2
 
-train3 = {key: value for key, value in train1.items()}
-train3['img_prefix'] = train_img_prefix3
-train3['ann_file'] = train_ann_file3
-train3['loader']['file_format'] = 'txt'
-train3['loader']['parser'] = dict(
-    type='LineStrParser',
-    keys=['filename', 'text'],
-    keys_idx=[0, 1],
-    separator=' ')
+train3 = dict(
+    type='OCRDataset',
+    img_prefix=train_img_prefix3,
+    ann_file=train_ann_file3,
+    loader=dict(
+        type='AnnFileLoader',
+        repeat=1,
+        file_format='txt',
+        parser=dict(
+            type='LineStrParser',
+            keys=['filename', 'text'],
+            keys_idx=[0, 1],
+            separator=' ')),
+    pipeline=None,
+    test_mode=False)
 
 train_list = [train1, train2, train3]