Bug 1917245 - Mark test as intermittent, r=aryx

Seems to timeout on my machine, so probably not a perma-pass on opt as
the bug suggests.

Differential Revision: https://phabricator.services.mozilla.com/D221470

Author: jgraham

testing/web-platform/meta/css/css-view-transitions/transition-skipped-from-invalid-callback.html.ini

@@ -1,4 +1,4 @@
 [transition-skipped-from-invalid-callback.html]
-  expected: TIMEOUT
+  expected: [OK, TIMEOUT]
   [transition skipped because callback has invalid syntax]
-    expected: TIMEOUT
+    expected: [PASS, TIMEOUT]