Update animation shorthand test to use .
We expect that we don't accept timeline name in the shorthand for now,
so we should use a valid syntax of timeline name for test.
Differential Revision: https://phabricator.services.mozilla.com/D216844
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1908357
gecko-commit: 73216b85bd3ca76afa8637be6782bfa4da1aabf1
gecko-reviewers: firefox-style-system-reviewers, layout-reviewers, emilio