add error_context() to groups.py and nodes.py

groups.py

@@ -1,7 +1,10 @@
 from os.path import join
 from pathlib import Path
 
+from bundlewrap.utils import error_context
+
 groups = {}
 for group in Path(join(repo_path, "groups")).rglob("*.py"):
+    with error_context(filename=str(group)):
         with open(group, 'r') as f:
             exec(f.read())

nodes.py

@@ -4,8 +4,10 @@ from pathlib import Path
 
 import bwpass
 from bundlewrap.metadata import atomic
+from bundlewrap.utils import error_context
 
 for node in Path(join(repo_path, "nodes")).rglob("*.py"):
+    with error_context(filename=str(node)):
         with open(node, 'r') as f:
             exec(f.read())