bpo-42195: Disallow isinstance/issubclass for subclasses of genericaliases in Union (GH-24059)

Previously this didn't raise an error. Now it will:
```python
from collections.abc import Callable
isinstance(int, list | Callable[..., str])
```
Also added tests in Union since there were previously none for stuff like ``isinstance(list, list | list[int])`` either.

Backport to 3.9 not required.

Automerge-Triggered-By: GH:gvanrossum

1 files changed, 1 insertions, 1 deletions

diff --git a/Objects/unionobject.c b/Objects/unionobject.c
index 32aa507..0535036 100644
--- a/Objects/unionobject.c
+++ b/Objects/unionobject.c
@@ -34,7 +34,7 @@ is_generic_alias_in_args(PyObject *args) {
     Py_ssize_t nargs = PyTuple_GET_SIZE(args);
     for (Py_ssize_t iarg = 0; iarg < nargs; iarg++) {
         PyObject *arg = PyTuple_GET_ITEM(args, iarg);
-        if (Py_TYPE(arg) == &Py_GenericAliasType) {
+        if (PyObject_TypeCheck(arg, &Py_GenericAliasType)) {
             return 0;
         }
     }