allow CSS to override Markdown tables

Author: willmcgugan

src/textual/widgets/_markdown.py

@@ -649,7 +649,7 @@ def __init__(self, headers: list[Content], rows: list[list[Content]]):
     def pre_layout(self, layout: Layout) -> None:
         assert isinstance(layout, GridLayout)
         layout.auto_minimum = True
-        layout.expand = True
+        layout.expand = not self.query_ancestor(MarkdownTable).styles.is_auto_width
         layout.shrink = True
         layout.stretch_height = True