setup.py: fix version parsing on Python 3.14 (ast.Str removed)

Python 3.14 removes the ast.Str node type. String literals now appear
as ast.Constant(value=str).
Update the AST check to accept both ast.Str (for older Pythons) and
ast.Constant with a string value (for Python 3.8+), allowing html5lib to
build successfully on Python 3.14 while remaining compatible with older
version.

Author: sookach

setup.py

@@ -92,9 +92,14 @@ def default_environment():
     for a in assignments:
         if (len(a.targets) == 1 and
                 isinstance(a.targets[0], ast.Name) and
-                a.targets[0].id == "__version__" and
-                isinstance(a.value, ast.Str)):
-            version = a.value.s
+                a.targets[0].id == "__version__"):
+            if hasattr(ast, "Str") and isinstance(a.value, ast.Str):
+                version = a.value.s
+            elif (hasattr(ast, "Constant")
+                  and isinstance(a.value, ast.Constant)
+                  and isinstance(a.value.value, str)):
+                version = a.value.value
+assert version is not None
 
 setup(name='html5lib',
       version=version,