ci: Fix formatting

At the same time, reduce indentation level on lists because otherwise the formatter is broken.

tools/yamlfmt

@@ -4,7 +4,8 @@
 Usage: yamlfmt.py [--apply] file.yaml
 """
 
-import ruamel.yaml
+import io
+from ruamel.yaml import YAML
 import sys
 
 args = sys.argv[:]
@@ -16,10 +17,16 @@ except ValueError:
 
 path = args[1]
 
+def dump(yaml, yml):
+    buf = io.BytesIO()
+    yaml.dump(yml, buf)
+    return buf.getvalue().decode('utf-8')
+
 with open(path) as f:
     contents = f.read()
-    yml = ruamel.yaml.round_trip_load(contents)
-    formatted = ruamel.yaml.round_trip_dump(yml, block_seq_indent=2)
+    yaml = YAML()
+    yml = yaml.load(contents)
+    formatted = dump(yaml, yml)
     well_formatted = formatted == contents
         
 if not well_formatted: