Update train.py

As see in ultralytics#6463, modification on train in evolve process to allow custom save directory.

train.py

@@ -474,7 +474,7 @@ def parse_opt(known=False):
     parser.add_argument('--optimizer', type=str, choices=['SGD', 'Adam', 'AdamW'], default='SGD', help='optimizer')
     parser.add_argument('--sync-bn', action='store_true', help='use SyncBatchNorm, only available in DDP mode')
     parser.add_argument('--workers', type=int, default=8, help='max dataloader workers (per RANK in DDP mode)')
-    parser.add_argument('--project', default=ROOT / 'runs/train', help='save to project/name')
+    parser.add_argument('--project', help='save to project/name')
     parser.add_argument('--name', default='exp', help='save to project/name')
     parser.add_argument('--exist-ok', action='store_true', help='existing project/name ok, do not increment')
     parser.add_argument('--quad', action='store_true', help='quad dataloader')
@@ -515,7 +515,8 @@ def main(opt, callbacks=Callbacks()):
             check_file(opt.data), check_yaml(opt.cfg), check_yaml(opt.hyp), str(opt.weights), str(opt.project)  # checks
         assert len(opt.cfg) or len(opt.weights), 'either --cfg or --weights must be specified'
         if opt.evolve:
-            opt.project = str(ROOT / 'runs/evolve')
+            if opt.project=='None':
+                opt.project = str(ROOT / 'runs/evolve')
             opt.exist_ok, opt.resume = opt.resume, False  # pass resume to exist_ok and disable resume
         opt.save_dir = str(increment_path(Path(opt.project) / opt.name, exist_ok=opt.exist_ok))