Bug 1705443 - Use vsync priority in PIntrPriority::Msg r=smaug

We've renamed the `high` priority to `vsync` in bug 1697585,
this is just adapting the change.

Differential Revision: https://phabricator.services.mozilla.com/D112198

ipc/ipdl/test/ipdl/error/PIntrPriority.ipdl

@@ -2,5 +2,5 @@
 
 intr protocol PIntrPriority {
 child:
-  [Priority=high] intr Msg();
+  [Priority=vsync] intr Msg();
 };