Fix typo

Author: 1-1sam

t/run/todo.t

@@ -110,7 +110,7 @@ TODO: {
         print $x->{ new }[0];
         EOF
     is($?, 0, "No assertion failure");
-    is($results, 'mana', 'push on non-existant hash entry from ternary autovivifies array ref');
+    is($results, 'mana', 'push on non-existent hash entry from ternary autovivifies array ref');
 
     $results = fresh_perl(<<~'EOF', {});
         my $x = { arr => undef };