Added test case

Author: otethal

graalpython/com.oracle.graal.python.test/src/tests/cpyext/test_unicode.py

@@ -674,6 +674,7 @@ class TestPyUnicode(CPyExtTestCase):
             ("%s, %r", ("hello", "world")),
             ("nothing else", tuple()),
             (UnicodeSubclass("%s, %r"), ("hello", "world")),
+            ("%d.%d", (42, 123)),
         ),
         resultspec="O",
         argspec='OO',