fix: isinstance narrowing regression with dynamic tuple argument

mypy/checker.py

@@ -8028,7 +8028,22 @@ def get_type_range_of_type(self, typ: Type) -> TypeRange | None:
 
         if isinstance(typ, UnionType):
             type_ranges = [self.get_type_range_of_type(item) for item in typ.items]
-            item = make_simplified_union([t.item for t in type_ranges if t is not None])
+            if any(t is None for t in type_ranges):
+                return None
+            # Filter out None and UninhabitedType entries (type checkers need explicit None check)
+            valid_ranges = [
+                t
+                for t in type_ranges
+                if t is not None and not isinstance(get_proper_type(t.item), UninhabitedType)
+            ]
+            if not valid_ranges:
+                return TypeRange(UninhabitedType(), is_upper_bound=False)
+            # If the only meaningful type we can extract is "object", we've lost
+            # type precision (e.g. from a widened _ClassInfo alias). Return None
+            # to avoid narrowing to a useless type.
+            item = make_simplified_union([t.item for t in valid_ranges])
+            if isinstance(item, Instance) and item.type.fullname == "builtins.object":
+                return None
             return TypeRange(item, is_upper_bound=True)
         if isinstance(typ, FunctionLike) and typ.is_type_obj():
             # If a type is generic, `isinstance` can only narrow its variables to Any.