Handle error on __repr__ for exceptions sequence passed to ExceptionGroup()

Author: dr-carlos

Objects/exceptions.c

@@ -909,6 +909,13 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     /* Save initial exceptions sequence as a string incase sequence is mutated */
     if (!PyList_Check(exceptions) && !PyTuple_Check(exceptions)) {
         exceptions_str = PyObject_Repr(exceptions);
+        if (exceptions_str == NULL) {
+            /* We don't hold a reference to exceptions, so clear it before
+             * attempting a decref in the cleanup.
+             */
+            exceptions = NULL;
+            goto error;
+        }
     }
 
     exceptions = PySequence_Tuple(exceptions);
@@ -997,7 +1004,7 @@ BaseExceptionGroup_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     self->excs_str = exceptions_str;
     return (PyObject*)self;
 error:
-    Py_DECREF(exceptions);
+    Py_XDECREF(exceptions);
     Py_XDECREF(exceptions_str);
     return NULL;
 }