Fix grid shorthand parsing to not incorrectly ignore the last token i…

…n one case.

Differential Revision: https://phabricator.services.mozilla.com/D149666

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1774791
gecko-commit: 77dca66144deaff050008026c46ad56df2e88838
gecko-reviewers: dholbert

css/css-grid/parsing/grid-shorthand-invalid.html

@@ -46,6 +46,7 @@
 test_invalid_value("grid", 'auto-flow / auto-flow');
 test_invalid_value("grid", 'auto-flow 1fr / auto-flow 1fr');
 test_invalid_value("grid", 'dense auto-flow / dense auto-flow');
+test_invalid_value("grid", 'auto / auto-flow foo()');
 // FIXME: add more values to test full syntax
 
 </script>