bpo-40491: Fix typo in syntax error for numeric literals (GH-19893)

diff --git a/Parser/pegen/pegen.c b/Parser/pegen/pegen.c
index 9858f71..391f9b9 100644
--- a/Parser/pegen/pegen.c
+++ b/Parser/pegen/pegen.c
@@ -907,7 +907,7 @@
 
     if (p->feature_version < 6 && strchr(num_raw, '_') != NULL) {
         p->error_indicator = 1;
-        return RAISE_SYNTAX_ERROR("Underscores in numeric literals are only supported"
+        return RAISE_SYNTAX_ERROR("Underscores in numeric literals are only supported "
                                   "in Python 3.6 and greater");
     }