py-soupsieve: updated to 1.9.1

1.9.1
- **FIX**: :root, :contains(), :default, :indeterminate, :lang(), and :dir() will properly account for HTML
iframe elements in their logic when selecting or matching an element. Their logic will be restricted to the document
for which the element under consideration applies.
- **FIX**: HTML pseudo-classes will check that all key elements checked are in the XHTML namespace (HTML parsers that do
not provide namespaces will assume the XHTML namespace).
- **FIX**: Ensure that all pseudo-class names are case insensitive and allow CSS escapes.

(adam)