doc: fix EncodingWarnings in examples (#11158)

Otherwise the warnings show in the regen output.

doc/en/example/nonpython/conftest.py

@@ -12,7 +12,7 @@ class YamlFile(pytest.File):
         # We need a yaml parser, e.g. PyYAML.
         import yaml
 
-        raw = yaml.safe_load(self.path.open())
+        raw = yaml.safe_load(self.path.open(encoding="utf-8"))
         for name, spec in sorted(raw.items()):
             yield YamlItem.from_parent(self, name=name, spec=spec)