Bug 1908357 - Update animation shorthand test to use <dashed-ident>. r=firefox-style-system-reviewers,layout-reviewers,emilio

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

testing/web-platform/meta/scroll-animations/css/animation-shorthand.html.ini

@@ -7,7 +7,7 @@
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1824261
     expected: FAIL
 
-  [e.style['animation'\] = "1s linear 1s 2 reverse forwards paused anim timeline" should not set the property value]
+  [e.style['animation'\] = "1s linear 1s 2 reverse forwards paused anim --timeline" should not set the property value]
     bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1824261
     expected: FAIL
 

testing/web-platform/tests/scroll-animations/css/animation-shorthand.html

@@ -20,7 +20,7 @@ test_invalid_value('animation',
 test_invalid_value('animation',
   '1s linear 1s 2 reverse forwards paused anim view()');
 test_invalid_value('animation',
-  '1s linear 1s 2 reverse forwards paused anim timeline');
+  '1s linear 1s 2 reverse forwards paused anim --timeline');
 
 test_computed_value('animation',
   '1s linear 1s 2 reverse forwards paused anim');