PyUnicode_FromFormatV(): Fix %A format

It was not completly implemented. Add a test.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 0e2f950..7564b67 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1074,6 +1074,7 @@
             }
             case 'S':
             case 'R':
+            case 'A':
             {
                 Py_UNICODE *ucopy;
                 Py_ssize_t usize;