bpo-35224: Add support for NamedExpr to unparse.py (GH-11670)

diff --git a/Tools/parser/unparse.py b/Tools/parser/unparse.py
index 82c3c77..70b47a1 100644
--- a/Tools/parser/unparse.py
+++ b/Tools/parser/unparse.py
@@ -79,6 +79,13 @@
         self.fill()
         self.dispatch(tree.value)
 
+    def _NamedExpr(self, tree):
+        self.write("(")
+        self.dispatch(tree.target)
+        self.write(" := ")
+        self.dispatch(tree.value)
+        self.write(")")
+
     def _Import(self, t):
         self.fill("import ")
         interleave(lambda: self.write(", "), self.dispatch, t.names)