[MRG] _return_root_paths now only looks in subfolders of root starting with 'sub-'

mne_bids/path.py

@@ -2441,7 +2441,8 @@ def _return_root_paths(root, datatype=None, ignore_json=True):
     else:
         paths = [p for p in paths if p.is_file()]
 
-    # only keep files which are of the form root/sub-*, such that we only look in 'sub'-folders
+    # only keep files which are of the form root/sub-*,
+    #  such that we only look in 'sub'-folders:
     root_sub = str(root / "sub-")
     paths = [p for p in paths if str(p).startswith(root_sub)]