fix: update MathML test

Author: sto3psl

packages/vue/__tests__/mathmlNamespace.spec.ts

@@ -5,6 +5,7 @@
 // - runtime-core/src/renderer.ts
 // - compiler-core/src/transforms/transformElement.ts
 
+import { vtcKey } from '../../runtime-dom/src/components/Transition'
 import { render, h, ref, nextTick } from '../src'
 
 describe('MathML support', () => {
@@ -69,7 +70,10 @@ describe('MathML support', () => {
     const f2 = document.querySelector('#f2')!
     expect(f1.getAttribute('class')).toBe('foo')
     expect(f2.className).toBe('foo')
-    ;(f2 as any)._vtc = ['baz']
+
+    // set a transition class on the <div> - which is only respected on non-svg
+    // patches
+    ;(f2 as any)[vtcKey] = ['baz']
     cls.value = 'bar'
     await nextTick()
     expect(f1.getAttribute('class')).toBe('bar')