Bug #1588287: fix invalid assertion for `1,2` in debug builds.

Will backport
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 69e1980..14ce7e4 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -747,6 +747,8 @@
 
         x = `x`
         x = `1 or 2 or 3`
+        self.assertEqual(`1,2`, '(1, 2)')
+
         x = x
         x = 'x'
         x = 123